Embryonic development and fecundity of thesquat lobster Munida gregaria (Decapoda:Galatheidae) in northern Patagonia

fernando gaspar dellatorre and ximena gonza’ lez-pisani

Centro Nacional Patagonico—Consejo Nacional de Investigaciones Cientıficas y Tecnicas, Brown Boulevard No. 2915, PuertoMadryn U9120ACF, Chubut, Argentina

In this study, fecundity of Munida gregaria in northern Patagonia was analysed in relation to size and compared with otherstudies in different sites along its latitudinal distribution. Also, morphological changes in embryos reared in the laboratory,and the chronology of its appearance were observed. Fecundity (total number of eggs in a clutch) was strongly correlated tosize (carapace length in mm) (R ¼ 0.638) and the regression equation fitted by least squares was Log(F) ¼ 21.37 + 3.85 .

log(CL). Size specific fecundity was higher than in southern locations along Patagonia. Recently extruded eggs are smallerthan in southern Patagonia measuring an average of 530 mm in diameter and 0.043 mm3 in volume. When ready tohatch, those measures increased by 30% and 50% respectively. Complete embryonic development lasted an average of 27.9days at fixed temperature of 118C. Five development stages were defined based on morphological changes: (1) from fertiliza-tion to the appearance of embryonic primordium (2–3.5 days); (2) embryonic tissues occupying less than half of the egg per-imeter in lateral view (7–10 days); (3) embryonic tissues without pigments and occupying more than half of the egg perimeterin lateral view (5–8 days); (4) embryos with reddish eye pigments and chromatophores (4–6 days); and (5) ocular globecompletely pigmented (3–4 days).

Keywords: embryology, fecundity, squat lobster, Munida gregaria, Patagonia

Submitted 8 August 2009; accepted 29 March 2010

I N T R O D U C T I O N

Squat lobsters (Decapoda: Anomura: Galatheidae) comprisemore than 200 small-sized species distributed worldwide,ranging from sublittoral to abyssal environments. Because oftheir high abundance, some galatheids represent an importantfood source, supporting large-scale fisheries (Longhurst, 1967;Castilla & Becerra, 1976; Roa et al., 1995) and populations ofseveral marine resources like crabs, squids, fish, whales, alba-trosses and penguins (Romero, 2003; Etnoyer et al., 2004;Longhurst, 2004). Munida is the only galatheid genuspresent in the south-western Atlantic. Fourteen species livebetween the equator and the La Plata River (368S)(Melo-Filho & Melo, 2001), and only two, Munida spinosa(Henderson, 1885) and Munida gregaria (Fabricius, 1793)have been reported to occur on the continental shelf fromthe La Plata River to the southern tip of South America(Cape Horn, 558S) (Spivak, 1997; Arntz et al., 1999).Munida spinosa inhabits deep waters on the shelf break andM. gregaria (¼M. subrugosa) (Perez-Barros et al., 2008) inha-bits coastal and shelf waters from Cape Horn to Valdes penin-sula (438S), and deeper shelf waters up to Uruguay (358S)(Spivak, 1997). Munida gregaria is simultaneously a depositfeeder and a predator on components of the fito and zoo-benthos, and is considered a key species in the Patagonian

shelf marine community representing ‘the direct link betweenthe detritus and the top predators’ (Romero et al., 2004) anda potentially exploitable fisheries resource (Lovrich et al.,1998; Wyngaard et al., 2001). Larvae of M. gregaria constitutean important fraction of the zooplankton biomass during latewinter and spring (Lovrich, 1999; Dellatorre, 2009).

Reproduction of M. gregaria has been studied along its lati-tudinal distribution (Tapella et al., 2002, 2005; Vinuesa, 2007;Dellatorre & Baron, 2008). Fecundity (considered as numberof eggs per clutch) is strongly correlated with female size. Inthe southern limit of its distribution (Beagle Channel (BC),558S), fecundity exceeds 10,000 eggs per brood in females27 mm in carapace length (CL) (Tapella et al., 2002;Vinuesa, 2007) while in San Jorge Gulf (SJG) (CentralPatagonia, 46–478S) fecundity is higher than 7000 eggs perbrood in females 22–23 mm in CL (Vinuesa, 2007). Tapellaet al. (2005) reported a similar relationship between femalesize (CL) and fecundity in those locations (without reportingthe regression model) but greater egg size in females from theBC, stating consequently that reproductive output (the ratiobetween the organic matter of the brood and the female) ishigher in the BC than in SJG. However, this study did not con-sider the possibility of multiple spawning events per female ina single reproductive season (reported later by Vinuesa, 2007;Dellatorre & Baron, 2008) to estimate the overall reproductiveinvestment. The seasonal sea surface temperature (SST)regime differs markedly between BC (monthly averageranging 4.2–9.88C) and SJG (monthly average ranging6.8–14.28C) (Dellatorre & Baron, 2008) and probablyexplains the greater size of eggs in southern populations.

Corresponding author:F.G. DellatorreEmail: dellatorre@cenpat.edu.ar

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Journal of the Marine Biological Association of the United Kingdom, page 1 of 10. # Marine Biological Association of the United Kingdom, 2010doi:10.1017/S0025315410000883

Also females reach 27 mm in CL in BC and only 23 mm in CLin SJG (Tapella et al., 2002; Vinuesa, 2007). This work is thefirst report about fecundity of M. gregaria from the northernlimits of its coastal distribution.

The breeding period of M. gregaria spans from May toSeptember in BC (Tapella et al., 2002). In SJG ovigerousfemales are found in high proportions from June to October(Vinuesa, 2007), while in Nuevo Gulf (NG) (42–438S) theyare present from June to November –December, in a surfacetemperature regime ranging seasonally from 9.68C to 17.28Cin the coldest and warmest month respectively (Dellatorre &Baron, 2008). Evidence of multiple spawning during thesame reproductive season was reported by Dellatorre &Baron (2008) based on the observation of ovaric re-maturationduring the breeding, and preliminary measures of embryonicdevelopment duration at fixed temperature conditions.Contrasting temperature regimes along the species range ofdistribution may affect the embryonic development time(Wear, 1974) and other reproductive traits like reproductiveseasonality, reproductive investment, fecundity and breedingcost (Fernandez & Brante, 2003).

Embryonic development has not been extensively studiedin galatheid crabs (Wear, 1974; Van Dover & Williams,1991) probably because most of the species belonging to thisfamily inhabit deep habitats (Melo-Filho & Melo, 2001) andbecause abortion of the entire egg masses during stressingmanipulation is a common behaviour (G. Lovrich, personalcommunication). Even though the embryonic developmentof M. gregaria has not been described in detail, incubationsin aquaria have allowed to estimate a duration of approxi-mately 29 days at constant temperature of 118C (Dellatorre& Baron, 2008). The description of morphological changesof embryos and its chronology can assist in future estimationsof breeding period, number of spawnings and hatchingperiods of M. gregaria, in different locations (Nagao et al.,1999).

The present work has two objectives: (1) to analyse thesize–fecundity relationship of M. gregaria from northernPatagonia and to compare it with those observed in areaswith contrasting thermal regimes: BC and SJG; and (2) todescribe the complete embryonic development of thespecies, illustrating the major embryonic features along withthe chronology of their appearance.

M A T E R I A L S A N D M E T H O D S

Munida gregaria specimens were captured in August 2004,from June to September 2005, in July 2006, and in July2007, using cylindrical collapsible crayfish traps deployed for1–2 days on the muddy sea bottom in two different sites(with 18 and 25 m depth and separated by 2 km) in NuevaBay (42.758S 65.008W, within Nuevo Gulf) (Figure 1).Fecundity, considered as the number of eggs per clutch, wasmeasured in 64 ovigerous females from all the sampledmonths, except in July 2007. Total number of eggs in theclutch was counted under binocular microscope on 41females. In the other 23 specimens, the egg clutch was care-fully separated from the female by cutting the base of eachpleopod, and eggs were individually removed from thepleopod setae with fine tipped forceps. Eggs were sieved andplaced on blotting paper to remove excess water. For eachfemale, the total clutch was weighed to the nearest 1 mg

using an analytical balance. Then, 10 to 30% of the eggs inthe clutch were taken apart, weighed and counted under bin-ocular microscope, and the number of eggs in the entire clutchwas extrapolated. Only recently spawned females (first twostages of embryonic development) captured during the firsthalf of the reproductive season (from June to September)were analysed, since multiple spawning may occur duringthe reproductive season (Dellatorre & Baron, 2008) andthere might be intra-seasonal variations in fecundity.

To study the embryonic development, 18 ovigerous femalesrecently spawned (10 females sampled in July 2006 andanother 8 females sampled in July 2007) were maintained in10 l plastic aquaria filled with seawater, and with constantaeration. Seawater temperature was maintained at 118C(+18C) because the mean surface temperature on coastalnorthern Patagonia (438S) during the breeding season(June to December) is 11.58C (SST data obtained fromsatellite estimations for the period 1987–1998; AVHRROceans Pathfinder NOAA–NASA). The crabs were fed adlibitum with hake (Merluccius hubbsi) meat every 2–6 days,and seawater was replaced every 4–6 days.

Every 2–6 days, a sample of five to ten developing embryos(representative of the entire clutch) was removed from thepleopods of each female using fine-tipped forceps, examinedunder a dissecting microscope at 25X magnification, andclassified into five categories of embryonic development(Table 1) (modified from Dellatorre & Baron, 2008). Themoment of change of embryonic stage was considered in the

Fig. 1. Southern coast of South America and Argentine Continental Shelf.Latitude (south) and longitude (west) are at right and lower marginsrespectively. LPR, La Plata River; VP, Valdes Peninsula; NG, Nuevo Gulf;NB, Nueva Bay; SJG, San Jorge Gulf; MS, Magellan Strait; BC, BeagleChannel; CH, Cape Horn.

2 fernando gaspar dellatorre and ximena gonza’ lez-pisani

middle of the period between observations in which suchchange was produced. Stage duration was expressed in daysand the average of stage duration was computed from allthe females that survived each entire stage (the average ofthe complete embryonic development duration was computedfrom three females that survived until hatching).

In order to describe morphological variations of embryosin detail, some of them were observed under a LeicaDFC280 light microscope equipped with differential contrastinterference optics. The external envelope (chorion) ofembryos was removed with fine-tipped forceps to obtain thebest view of the embryonic structures. Some of the appendageswere removed for observation at 200X in the stereoscopicmicroscope. Digital images were obtained with LeicaApplication Suite (Version 2.5 R1) software.

Another twenty-five females were captured in July 2007breeding embryos in different stages of development, andapproximately fifteen living eggs from each of these femaleswere measured using an ocular micrometer under 50X magni-fication. For those measures the following dimensions weredefined: (1) dorso-ventral diameter: between animal pole(where embryo develops) and vegetal pole (the opposite);and (2) antero-posterior diameter: perpendicular to dorso-ventral diameter, anterior part of the embryo is identified bythe ocular globe. The egg volume was estimated using theformula of an ellipsoid volume:

V = 4/3 × p× r1 × r2( )2

where V is the egg volume, r1 the half of the major diameter(antero-posterior) and r2 the half of the minor diameter(dorso-ventral) (Garcıa-Guerrero & Hendrickx, 2004). Oneach stage, the antennules, antennae, eyes, mouth parts,

abdomen, telson, carapace, rostral spine, posterior spinesand chromatophores were observed and described. The termi-nology used for embryonic appendages follows that used byClark et al. (1998) and Roberts (1973) for larval appendages.

R E S U L T S

Ovigerous females of M. gregaria ranging 9.3–20.5 mm in CL(N ¼ 64) carried between 32 and 7065 eggs attached on theirpleopods. The total number of eggs in the clutch (F) wasstrongly correlated with carapace length (CL, mm) (R ¼0.638) (Figure 2). The following model was fitted to the

Fig. 2. Relationship between size and fecundity. The black regression linerepresents the model adjusted to data from Nuevo Gulf, while the dottedline shows the regression model fitted by Tapella et al. (2002) to data fromthe Beagle Channel. The extension of both lines on the abscise axisrepresents the size-range sampled.

Table 1. General features of Munida gregaria embryos at each stage of embryogenesis.

General features Stage I Stage II Stage III Stage IV Stage V

Embryonic tissues Absent Embryonic primordium Occupies more than halfof the egg

Growing Completely formed

Antennule Absent Uniramous and flattened Uniramous and tubular Uniramous and tubular Uniramous and tubularAntenna Absent Uniramous and flattened Biramous and tubular Biramous and tubular Biramous and tubularMandible Absent Absent Visible Tubular and short Tubular and shortMaxillule Absent Absent Visible With an endopodite, a basal

endite and a coxal enditeWith an endopodite, a basal

endite and a coxal enditeMaxilla Absent Absent Visible With endites, palp and

scaphognathiteWith endites, palp and

scaphognathiteMaxilliped I Absent Uniramous and flattened Biramous and tubular Segmentation in the endo and

exopoditeSegmentation in the endo and

exopoditeMaxilliped II Absent Uniramous and flattened Biramous and tubular Segmentation in the endo and

exopoditeSegmentation in the endo and

exopoditeMaxilliped III Absent Absent Absent Absent RudimentaryPereopods Absent Absent Absent Absent AbsentPleopods Absent Absent Absent Absent AbsentAbdomen Absent Short and wide

projectionSegmented Five segments, the sixth is still

fused to the telsonWith lateral spine

Telson Absent Bilobulated Lobules with a sharp endand terminal spine

Spine are increasing in length Spine became plumose

Eye pigments Absent Absent Absent Appear Occupies the entire ocularglobe

Chromatophores Absent Absent Absent Appear in different bodyregions

Increase in number and size

Cephalothoracicspines

Absent Absent Detectable and short Long spines Long spines

embryonic development and fecundity of munida gregaria 3

relationship by least square regression:

Log(F) = −1.37 + 3.85 · log (CL)

The complete embryonic development lasted on average27.9 days (Table 2). Freshly spawned oocytes were adheredto the setae along each one of the four female pleopods.Stages of the embryonic development observed in Munidagregaria (Table 1) were as follows:

Stage IThis stage lasts between 2 and 3.5 days (Table 2). It beginsimmediately after fertilization, when the first divisions of theoocyte occur (Figure 3A). Two mutually adherent coveringssurround the embryo, forming the funiculus that holds theembryo to the pleopod setae (Figure 3A). The egg is sphericalin shape, with an average diameter of 530 mm (Table 2) andpresents a uniform dark green coloration. In the first hoursafter extrusion the egg chorion does not recover a sphericalshape easily when crumpled (during manipulation withforceps). Later, the cellular division forms the blastomers(Figure 3A). By the end of this stage, the morula can beobserved (Figure 3B). Within the oocyte, vitelline granulesare not common, and the embryo is not detectable.

Stage IIThis stage lasts 7–10 days and rounded eggs have a diametersimilar to the previous stage (Table 2). The embryonic pri-mordium appears as a small transparent zone at the animalpole of the zygote (Figure 3C), representing the ventralregion of the embryo. This area begins to deepen andextends in an antero-posterior direction. At the beginning ofthis stage, the outlines of the ocular globe can be discernedas flat smooth structures projecting dorso-laterally and thebud of the antennules and antennae can be observed as twopairs of extensions (Figure 3D). At the middle of this stagetwo pairs of mouth parts can be observed, all the appendagesare flattened and uniramous (Figure 3E). The cephalic zonethen arises, bearing four pairs of appendages. The posteriorthoraco-abdominal plate presents a short, wide projection,with its distal extremity bifurcated into two lobes of thefuture telson.

Stage IIIThe duration of this stage is between 5 and 8 days (Table 2).The beginning of this stage is defined as the moment atwhich embryonic tissues occupy more than half of the eggperimeter in lateral view (Figure 3F). The embryo growsalong the antero-posterior axis, the egg covering aquires anellipsoidal shape and increases the maximum diameter(Table 2). The cephalothorax and abdominal regions canbe clearly differentiated (Figure 3F). The appendages havegrown and differentiated markedly. The antennule andantenna grow caudally parallel with each other (Figure 4A).The antennule is uniramous and tubular with a shortmiddle seta and three long terminal setae on the exopod,while the endopod is absent. The biramous antenna is themost developed of the appendages; hence it is longer thanthe antennule. The endopodite is short, wide, with a single,subterminal, thickened seta. The exopodite is long, widewith nine setae, short and firm, forming a straight line onthe lateral– ventral border toward the terminal zone. Themouth appendages: mandibule, maxillule and maxilla, arevisible in this stage of development between the antennaand the first maxilliped. All of the mouth parts have thesame length and they do not overlap each other. The twopairs of maxillipeds are biramous and have grown markedlyin length toward the anterior zone of the embryo, presentingendopodite and exopodite of the same length. The endo-podite possesses three long terminal setae (Figure 3F).One rostral and two posterior spines can be observed. Therostral spine is curved ventrally toward the caudal regionalong the mid-line of the embryo. The posterior spinesarise from the posterior –ventral border of the cephalothoraxin a cephalic direction. At the end of this stage, the abdomenremains folded ventrally over the thoracic zone growingbetween the appendages toward the insertion of the mouthappendages. Five segments can be observed, the sixth isstill fused to the telson. The lobules of the telson present asharp end and six short terminal spines.

Stage IVThis stage lasts between 4 and 6 days, eggs are ellipsoidal andmaximum diameters continue increasing (Table 2). It beginswith the appearance of pigmentation in the ocular globe andthe chromatophores (Figure 4B). This pigmentation can be

Table 2. Duration of embryonic development stages of Munida gregaria and size of the eggs during embryogenesis. The range of stage duration is basedon estimations from different breeding females (number of females in parentheses). ∗, major diameter (antero-posterior) is reported. The egg volume wasestimated from antero-posterior and dorso-ventral measures of diameter assuming an ellipsoidal shape. Egg diameter measures were taken in eggs fromdifferent breeding females (number of females in parentheses). (1) and (2) egg diameter (mm) from San Jorge Gulf (Vinuesa, 2007) and Beagle Channel

(Tapella et al., 2002) respectively, standard deviation in parentheses.

Stage Development timein days

Size

Mean Range (N) Diameter in mm (SD) Volume in mm3 (SD) Eggs measured Diameter in SJG (1) Diameter in BC (2)

1 3.1 2–3, 5 (11) 530 (22.5) 0.043 (0.0084) 116 (6) 640 690 (60)2 9.1 7–10 (12) 524 (13.7) 0.042 (0.0030) 97 (5) 7703 7.1 5–8 (14) 583∗ (19.4) 0.050 (0.0042) 30 (2) 8404 5.0 4–6 (7) 648∗ (20.1) 0.054 (0.0041) 119 (8) 8805 3.6 3–4 (4) 701∗ (14.4) 0.065 (0.0038) 52 (4)Total 27.9 26–28 (3)

4 fernando gaspar dellatorre and ximena gonza’ lez-pisani

observed in the area posterior to the ocular globe, as a darkcurved line (Figure 4B). The reddish chromatophores arelocated in different parts of the embryos (Figure 4B). It canbe observed with a star-shape at the bases of the mandibuleand at the base of the maxilliped. Elongated chromatophorescan be observed around the digestive tube in the 28 and 58segment of the abdomen at the beginning of this stage(Figure 4C), and in all abdomen segments at the end. Thetelson presented two pairs of star-shaped chromatophoresaround the anus (Figure 4C).

All the buccal appendices overlap. The mandibule is sur-rounded by the maxillule and maxilla. The mandibule is

tubular and short, and presents molar process. The maxilluleshows an endopodite with four terminal setae, a basal enditewith six setae and a coxal endite with five setae. The maxillapresents four endites with respectively 6, 4, 4 and 4 setae.Seven setae can be observed on the palp and five terminalsetae on the scaphognathite. Segmentation can be observedon the maxillipeds. The endopodite presents five segmentsand the exopodite two segments. In the telson, the six pairsof spines are increasing in length at the same rate alongthe external border (Figure 4C). Cardiac movements canbe clearly observed in the dorso-posterior region of thecephalothorax.

Fig. 3. Photographs of embryonic stages I (A, B), II (C, D) and III (E, F) of Munida gregaria. Bt, blastomers; Ep, embryonic primordium; An, antennule; AnI,antenna; Og, ocular globe; Mxp, first maxilliped; Ab, abdomen; T, telson; V, vitellum.

embryonic development and fecundity of munida gregaria 5

Stage VThe duration of this stage is between 3 and 4 days (Table 2).The embryo is almost completely formed and ready to hatch(Figure 4D). Green vitellum droplets are located in thedorso-medial region of the cephalothorax and its diameterin lateral view is shorter than half of the egg diameter in thesame axis (Figure 4D). The eyes are large and sessile, andthe reddish-brown pigmentation of the ocular globe is ovalin shape (Figure 4D). By the end of this stage the embryosare easily separated from the pleopods and their external cov-ering becomes labile. Hatching is induced by touching thecovering with a dissecting needle. The uniramous antennulehas no segmentation and displays a plumose subterminalseta and 5 terminals setae (2 short and 3 long). The biramousantenna has a short and wide endopodite with a plumose sub-terminal seta and 8 lateral spines. The nine setae of the exopo-dite are plumose, forming a straight line on the lateral –ventralborder toward the terminal zone. The first maxilliped presentsa short coxa with 2 plumose setae, a long basis with 4 groupsof 3 plumose setae in the internal margin. The endopodite pre-sents 3, 2, 1, 2 and 5 plumose setae in the internal margin. Theexopodite presents 4 terminal plumose setae. The second pairs

present a short coxa without setae and a long base with 3 distalplumose setae. The endopodite presents 2, 2, 2 and 5 plumosesetae in the internal margin. The exopodite presents 4 term-inal plumose setae. The third pair is rudimentary. No pereo-pods can be observed.

The abdomen extends to the insertion of the antennule(Figure 4D). It has 5 segments with the sixth fused to thetelson. The segments present a row of small posterior–dorsal spines. The third and fourth segment presents a pairof lateral spines. The telson is bi-lobulated with 6 pairs of pos-terior plumose spines. Sporadic movement of the appendagesand abdomen can be observed, becoming more frequent nearthe time of hatching. At the end of the embryonic develop-ment the eggs are ellipsoidal in shape, their maximum diam-eter is about 30% greater than in recently extruded eggs, andthe volume has increased by approximately 50% (Table 2).

D I S C U S S I O N

The embryonic stages of the decapods can be distinguishedbased on different criteria (Garcıa-Guerrero & Hendrickx,

Fig. 4. Photographs of embryonic stages III (A), IV (B) and V (C, D) of Munidagregaria. F, funiculus; Ct, chromatophores; Sp, telson spines; Op, ocular pigments;∗ , indicates chromatophores. Other letters represent the same as in Figure 3.

6 fernando gaspar dellatorre and ximena gonza’ lez-pisani

2004, 2006; Gonzalez-Pisani et al., 2009). To differentiatestages in this study, we used the appearance of different mor-phological characters, primordia of appendages, pigmentationon the ocular globe and chromathophores, as well as the com-plete formation of the embryo. Other authors have definedembryonic stages of development based on: (1) the index ofocular globe pigmentation, which is useful in species wherepigmentation occurs gradually during a long period (overmore than 70% of the total incubation period) (Perkins,1972); and (2) the changes in the form of some structures orappendages (Tavonatti, 1998; Tavonatti & Dupre, 2001;Dupre, 2003). In M. gregaria, those criteria were not usedbecause the ocular pigmentation does not appear until theend of stage III, when more than half of the total incubationperiod has passed and also because the ocular pigmentationcompletes in approximately 5 days (less than 20% of thetotal development time). On the other hand, development ofthe appendages of this species does not allow definingembryonic stages of development as in the case of the anten-nae of Jasus frontalis (Tavonatti & Dupre, 2001).

Some of the embryonic structures of M. gregaria are similarto those observed in embryos of other anomuran crabs, as forexample the rostral and postero-lateral spines of the carapace(Boschi et al., 1967; Garcıa-Guerrero & Hendrickx, 2004;Fujita & Osawa, 2005; Garcıa-Guerrero et al., 2005;Hernandez et al., 2005; Cuesta et al., 2006) and the I, II andIII maxillipeds, the last appearing as rudiments at the end ofthe embryonic development (Garcıa-Guerrero & Hendrickx,2006). The eggs have an oval shape at the end of the develop-ment, probably caused by the increase in length of the appen-dages and the intake of water to the intra-chorionic space(Pandian, 1970; Lardies & Wehrtmann, 1996; Lopez et al.,1997; Hernandez & Palma, 2003; Garcıa-Guerrero &Hendrickx, 2006; Surot-Navarro, 2006), in contrast to otherbrachyuran embryos that have spherical eggs with minor vari-ations in shape throughout development (Nagao et al., 1999;Pinheiro & Hattori, 2003; Garcıa-Guerrero & Hendrickx, 2004).

The embryonic development of species belonging to thefamilies Galatheidae and Chirostylidae has not been investi-gated to date. Of the other two families included in the super-family Galatheoidea (Martin & Davis, 2001), the Aeglidae arestrictly freshwater organisms (Martin & Davis, 2001) andosmoregulatory adaptations (Charmantier, 1998) may gener-ate development features that will not be compared with thoseobserved in this work. The embryonic development of thePorcellanidae has been extensively studied (Gore, 1968,1971; Hernandez et al., 1998; Garcıa-Guerrero & Hendrickx,2004, 2006; Hernandez et al., 2005; Gonzalez-Pisani et al.,2009). Embryonic development of M. gregaria differs fromthat of porcellanids in some aspects. Antennae exopodites ofM. gregaria are wide and flat with short and firm setae, becom-ing long and flexible by the end of development. In contrast, inthe porcellanids exopodites are long and tubular, with shortand firm setae forming a straight line on the lateral–ventralborder toward the terminal zone (Gonzalez-Pisani et al.,2009). In M. gregaria all chromatophores appear simul-taneously, when approximately 70% of the embryonic develop-ment time has elapsed. In change, porcellanid chromatophoresappear a few days after the eye pigments (Gore, 1968, 1971;Hernandez et al., 1998; Garcıa-Guerrero & Hendrickx, 2004;Garcıa-Guerrero et al., 2006; Gonzalez-Pisani et al., 2009). Atthe end of development of M. gregaria third maxillipeds arerudimentary while in porcellanids these appendages are not

detectable. Moreover, in porcellanids the initially bilobulatedtelson acquires a spatulate shape, with a convex distal border,while in M. gregaria it remains bilobulated, each lobule display-ing a sharp distal portion at the end of development. This lastfeature, and the cephalothoracic spines, allows the clear dis-tinguishing of larval forms of both families in planktonsamples (Dellatorre, 2009).

The length of the embryonic development of M. subrugosa(¼M. gregaria) has been a matter of speculation for severalyears. Rodrıguez & Bahamonde (1986) expected that itwould last 8–9 months in the Magellan Strait (SouthAmerica, 548S) and Tapella et al. (2002) stated that femaleshold their eggs over a period of three to four months in theBeagle Channel. Based on the monthly variations of theproportions of ovigerous females and stages of embryonicdevelopment, Vinuesa (2007) proposed that embryonic devel-opment would take 90 days in females spawning in July and70–80 days in females spawning in September in San JorgeGulf. Dellatorre & Baron (2008) provided the first data onthe length of the embryonic development, ranging in the lab-oratory from 26 to 29 days at 118C constant temperature. Ourresults confirm that M. gregaria embryos take approximately28 days from fertilization to hatching at 118C constanttemperature.

The embryonic development of galatheid crab species hasnot been described until present, and little information hasbeen published in regards to its length (Wear, 1974; VanDover & Williams, 1991; Tapella et al., 2002; Vinuesa,2007). Temperature is a key abiotic factor affecting theincubation of embryos. Typically, increased temperaturesshorten the duration of embryogenesis in decapod crustaceans(Perkins, 1972; Wear, 1974; Petersen, 1995; Tong et al., 2000;Smith et al., 2002; Hamasaki, 2003; Wehrtmann & Lopez,2003; Stevens et al., 2008). Some of those authors developedpredictive models of embryonic development time as functionof water temperature (Wear, 1974; Hamasaki, 2003;Wehrtmann & Lopez, 2003). The work of Wear (1974) isthe only one dealing with galatheid species in temperatewaters, and this makes the work adequate for comparisonwith our results. This author developed an equation to esti-mate the duration of embryonic development of Galatheadispersa at different temperatures based on aquarium incu-bations at four different constant thermal regimes (at 9, 12,18 and 218C). According to this equation, G. dispersa wouldincubate their embryos during 37 days at 118C constanttemperature. Assuming that the curve of the temperature–incubation period relationship has a similar shape forM. gregaria, we can recalculate the ‘biological zero’ or alphaparameter (Wear, 1974) and estimate the duration of embryo-nic development of M. gregaria at average ambient tempera-tures in the species habitat along its latitudinal distributionrange along the south-western Atlantic coast. Under thisassumption, the embryonic development of M. gregariawould last between 35 and 42 days in the San Jorge Gulf,where sea surface temperature (SST) ranges between 8.5 and9.58C during reproductive season, and approximately 75days in the Beagle Channel where SST averages 5.58Cduring reproductive season (SST data obtained from satelliteestimations for the period 1987–1998; AVHRR OceansPathfinder NOAA–NASA).

Egg size (diameter and volume) is smaller in Nuevo Gulfthan in San Jorge Gulf (Vinuesa, 2007) and the BeagleChannel (Tapella et al., 2002, 2005). This probably reflects

embryonic development and fecundity of munida gregaria 7

species adaptations to contrasting temperature regimes inthose locations (Fischer, 2009). Egg size increments inhigher latitudes would result in a shortened larval develop-ment and would reflect an adaptation to a short temporalwindow with nutritional and physical parameters optimalfor larval survival. This is generally known as the Thorson’srule (Thorson, 1950). On the other hand, the reduction inegg size increases surface:volume ratio, and this could com-pensate for the increases in breeding cost (mostly derivedfrom ventilation of egg clutch) when temperature increases(Fernandez & Brante, 2003). Intraspecific latitudinal vari-ations of egg size has been recorded in Cancer setosus(Brante et al., 2003), Pinnaxodes chilensis (Lardies &Castilla, 2001) and other brachyuran species (Brante et al.,2004). Smaller and lighter embryos at the lower latitudesmay reflect thermal adaptation to higher mean temperatures(Brante et al., 2003; Fischer, 2009). Those increments in eggsize with latitude would increase the length of embryonicdevelopment and bias our previous estimations (Wear,1974). Clutch size of decapods is limited morphometricallyby the space available for yolk accumulation in their rigidcephalothorax (Hines, 1982, 1992), which predicts a positiverelationship between fecundity and female size. This predic-tion is true for M. gregaria along its latitudinal distribution(Tapella et al., 2002, 2005; Vinuesa, 2007; present study).Considering this morphological limitation for the clutch sizeand assuming the same proportion of energy invested in eggproduction (for a single clutch), an inverse relationshipbetween egg size and fecundity can be expected (Hines,1982; Clarke, 1987). This tradeoff between egg size andfecundity occurs in M. gregaria, as in other decapod specieslike porcellanid crabs (Lardies & Wehrtmann, 1996), com-mensal crabs (Lardies & Castilla, 2001) and shrimps(Lardies, 1995); but in some other cases increments in eggsize and fecundity are observed simultaneously (Jones &Simons, 1983).

Temperature is the most important factor affectingembryonic development and reproductive strategies inmarine invertebrates (Vernberg, 1962). High temperaturemay increase growth rate and other metabolic activities redu-cing available energy for reproduction of some decapodspecies in lower latitudes (Jones & Simons, 1983) impedingthe tradeoff between egg size and fecundity predicted byHines (1982). This may not be the case of M. gregaria andfecundity (estimated as the number of eggs per clutch)seems to be constrained only by morphological factors.Nevertheless, more information is necessary to estimate theoverall reproductive investment of M. gregaria along its latitu-dinal distribution considering successive spawnings duringthe same reproductive season (Dellatorre & Baron, 2008)and the breeding costs (Fernandez et al., 2000).

A C K N O W L E D G E M E N T S

Experiments were performed in the Centro NacionalPatagonico, and partially funded by projects PICT 14700(ANPCyT) and PIP 5835 (CONICET). The authors werefully supported by doctoral fellowships from the CONICET.We are grateful to our advisor Dr Pedro Baron, who hasguided our doctoral research and improved an early versionof this manuscript. An anonymous referee greatly improvedthis manuscript with constructive comments.

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Correspondence should be addressed to:F.G. DellatorreCentro Nacional Patagonico—Consejo Nacionalde Investigaciones Cientıficas y TecnicasBrown Boulevard No. 2915Puerto Madryn U9120ACFChubut, Argentinaemail: dellatorre@cenpat.edu.ar

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