Freshwater Biology (\990) 23, 491-503

Growth and reproduction in the freshwater crah, fluviatile (, Brachyura)

FIORENZA MICHELI, FRANCESCA GHERARDI and MARCO VANNINI Department of Biology and Genetics, University of Florence, Italy

SUMMARY. 1. The patterns of relative and absolute growth and the reproductive biology of the freshwater Potamoti fluviatile were stud- ied in a natural population inhabiting a hill stream close to Florence, Italy, over an annual cycle. Periodical inspections of a stretch of the stream were made and morphological and anatomical analysis carried out. 2. As in other decapods, the females are smaller than the males (they can however occasionally reach larger dimensions). This may be determined by a lengthening of the moulting interval in the females, by their higher energetic cost of reproduction (since reproduction occurs simultaneously with moulting, at least in this habitat) and/or by a higher mortality rate resulting from the risks associated with carrying and vagility. 3. The analysis of relative growth in secondary sexual characters (abdomen width and major chela length) with respect to carapace length, shows that the pre-puberty and puberty ecdysis occur at 15 and 35 mm carapace length respectively, which was also confirmed by the gonad weight, vas deferens in males, and the onset of vitcllogenesis in females. 4. A delay between anatomical and functional (i.e. the ability to copul- ate successfully) maturity was observed in the males. Being larger may be an advantage in intra-sexual for mating, but larger males, being more vagile. are also more likely to meet receptive females. The females may mate before their puberty moult and store sperms in iheir seminal receptacles for when they attain full maturity; this could be adapt- ive since opportunities of encountering males are few and far between in their adult phase, characterized by their vagile and amphibious habits.

Introduction moult increment or growth factor and the inter- moult period or moult interval; Hartnoil, 1982) If the study of relative growth (that is the change can undoubtedly heip analysis of the population of shape as grow) throws light on the life structure. Though relative growth is obviously history of a given species, information on the nol an exclusive feature of , the pre- absolute growth patterns (determined by the sence of a rigid integument and thus the pos- sibility of accurate measurements, together with Correspondence: M. Vannini, Depanmenl of Animal the discontinuous growth pattern, make this Biology and Genetics. University of Florence, V. group an ideal object for allometric studies Romana 17. 50125 Florence. Italy. (Teissier. 1960; Hartnoil. 1982).

491 492 F. Micheli. F. Gherardi and M. Vannini

The most relevant changes in shape (apart During these inspections, the following mor- from those connected with larval life) take place phometrical data were taken: carapace length with the attainment of sexual maturity, often (CL) and width, width of the sixth abdominal accomplished at one particular moult, the segment, and length, width and height of chelae puberty moult (Perez. 1928), after which chelae, (Fig. 1). Measurements were also made of newly abdomen and pleopods (the secondary sexual moulted Individuals, including exuviae, when characters) are seen to follow differential growth they were found near the moulted animal. rates (Hartnoli, 1978). Ovigerous females and mating pairs were also In some eases, predictions of the attainment of recorded. Other morphometrical data, i.e. sexual maturity made on the basis of mor- abdomen and gonopod lengths, were taken from phometrical analysis have been confirmed by animals sacrificed for gonad examination. anatomical (Finney & Abeie, 1981)or histologi- About thirty-five specimens for dissection cal (Haley. 1969. 1973) examinations. Only a were collected from the stream once a month few works examine growth patterns as well as during 1986-87 and transferred to the labora- reproductive cycles (Haley, 1969; Finney & tory, where they were killed with chloroform Abele. 1981; Vannini & Gherardi, 1988). within a few hours and weighed, The weight of Scattered references exist on population the gonads from males and females, the colour structure and allometry of the secondary sexual of the ovaries and mean oocyte diameter (calcu- characters for , in Potamon gedro- lated from the measurements of about ten ran- sianum Alcock from Afghanistan (Schneider, domly chosen oocytes under the binocular 1971), and Geotetphusa dehanni White from microscope) were recorded. Samples of ovaries Japan (Yamaguchi & Takamatsu. 1980). or to and seminal receptacles were fixed in Camoy's the attainment of sexual maturity, in fluid and embedded in polystyrene resin. Sec- Barytetphusa guerini Milne Edwards from tions (7 fim thick) were stained using the India (Gangotri, Vasantha & Venkatachari, haemalum--eosin technique in order to check for 1978). Data on the population structure of the presence of sperm in the seminal receptacles Potamon fltiviatite Herbst have already been or of yolk inside the oocytes. As a criterion of published (Gherardi, Guidi & Vannini, 1987). anatomical sexual maturity in mates, the pre- In the present work, the patterns of absolute and sence of sperm in the vas deferens was adopted. relative growth are considered, together with Deferens tubules (from either freshly dissected gravimetric and histological analysis of the or fixed gonads) were dipped in distilled water gonads, which allows identification of the and broken with forceps, then examined under puberty moult. The interaction between moult the microscope. and reproductive cycles and their effects on the Sex-ratio at birth was determined in five population structure are also discussed. broods. About 50% of specimens from each brood were examined under a binocular micro- scope: buds of four pairs of pleopods are visible Materials and Methods in newly hatched females, whilst there are only two in males. is the only representative of The text gives mean values ± standard error. the in Italy, occurring from and southwards, included (Gherardi ef at., 1987). Fieldwork was con- Results ducted along a hill stream near Florence (170 m above sea level, mean width approximately 2 m, Absolute growth depth ranging from 10 to 90 cm, though greatly Ecdysis was principally restricted to early variable with the seasons). autumn (Fig. 2); animals in the early instars In order to determine the timing of the main probably moult more frequently (soft individ- events of the life cycle, a 150 m stretch of the uals smaller than 20 mm CL were found all year stream was periodically inspected from July to round, especially in autumn and spring). October 1986. No breeding females or moulting The correlation between per cent increment at animals (except some juveniles) were seen dur- moult (i.e. the percentage by which the posl- ing all the other periods of the year. moult length exceeds the pre-moult length; Growth and reproduction in a 493

AL

C W

FIG. 1. A diagram of P. ftuviatite showing some of the measurements taken (CL-carapace length; CW=carapace width; AL=abdomen length; AW = abdomen width; PL=claw propodite length; PW=daw propodiic width; PH=claw propodite height).

% 100-1

to-

M -

JULV AUGUST SEPTEMBER FIG. 2. Time of moulting (per cent of moulting ani- mals found is transects along the stream from June to Seplember.

10- Mauchline, 1976) and CL was not quite signifi- cant (males; meanvalue=I6.1±1.5%;r=0.466, df=IO, ns; females; mean value=15.5±1.12%; 25-3S /-=0.338. df=n, ns; males v. females; f=0.32, SIZE RA^GE df=23. ns). •MALES A significant difference existed between the 84 FIG. 3. Size-frequency distribution of moulting males size of moulting and hard animals (Fig. 3), males and females. of the former more frequently being smaller than 25 mm CL (/^ = 9.757. df=2, /'<0.0I), sexes ix^=\.24, df=l, ns). The difference be- whilst moulting females fell more in the range of tween sexes was not signficant for animals 25-35 mm CL (x^=^4.\21, df-2. /'<0.001). smaller than 25 mm CL either (/' = O.I04.df= I. Moult frequency dropped dramatically after ns), although it was so in the size range 23-35 35 mm CL, with no difference between the mm (/'=5.247, df- 1, P<0.05). 494 F. Micheti, F. Gherardi and M. Vannini

TABLE I. Paitcms of relative growth, /'=rcgrcssion coefficient (•/'<0.05; **/'

In (CL) v. N i (b*l) N i (69*1) n (CW) 343 .023 10.97* 305 ,025 6.88* • 0.37 In (MPL) 229 .262 35.79* 153 .217 15.39*' 2.90** In (mPL) 228 ,176 25,11* 155 .152 4.09*" 0.81 In (MPW) 231 .364 32,48* 155 .411 17.73** 1.95 In (mPW) 231 .205 16.80* 155 ,179 7.39** 1.02 In (MPH) 231 .314 31.57* 154 .354 10.16** 1.36 In (mPH) 231 .140 14.72* 154 ,11 5.66** 1.43 n (AL) 8 .570 6.84* 11 .014 0.26 5.70** In AW) 206 ().935 4.63* 235 .928 32.27** 32.36" ln (BWt) 16 :J.836 38.22* 15 i.693 17.60" 1.25

In (CL) v: N b N b MPL/mPL 226 0.085 16.35* 153 0,066 1.82 0.68

TABLE 2. Relative growth of pleopods

In (CL) v: df b () In (female pleopods) 1st cndopod. 8 1.385 3.I69** cxopod. 8 2.112 n.644** 2nd endopod. 8 1.617 5.268« cxopod. 8 2.182 11.491 •• 3rd endopod 7 1.513 2.952• cxopod. 8 1.806 2.650* 4tl) endopod. 7 1.563 3.545*" exopixl. 8 1.980 IO.741'» In (male pleopods) 1st ploepod. 19 1.161 2.101 2nd pleopod. 15 0.897 1.253

The total number of moulting animals, com- Relative growth pared with that of the non-moulting ones, did not differ significantly between the sexes (males: Carapace width, length, width and height of 27.38%; females: 31%; males v. females: both chelae, degree of heterochely. abdomen f={).\A.6i=\. ns). length and width, total body weight, and length Adults do not moult every year: of the animals of female pleopods all showed allometric growth marked in autumn 1985, by gluing plastic tags relative to CL (Tables 1 and 2). Bilogarithmic onto their carapaces (see Gherardi et at.. 1987) tranformation was used (Huxley, 1932; Hartnoll, and captured the following year slill carrying 1974). and CL was referred to as the independent their markers. 8% of males and 10% of females variable (Gray & Ncwcombe, 1938). had not moulted in autumn (all of them were Positive allometric growth of carapace width larger than 30 mm CL). versus CL was revealed with no difference Growth and reproduction in a freshwater crab 495

TABLE 3. Growth rate of major claw length (r In of carapace length) in diflercm instars (•/'<0.05; •'/'<0.0I) In (major claw length)

N b (6^1) Juveniles (

N b N b (ft^fel) (cfi?) Sub-adults (15-35 mm) 53 1.231 17.71'* 35 1.159 5.17** 2.45* Adults (>35 mm) 159 1.541 17.76* • 113 1.471 7.56" 1.11 Mates Females ; df df Juv. V. Sub-ad. 4.85*' 93 1.81 75 Sub-ad. V. Ad. 9.31"* 210 4.46" 146

between males and fctnales, and in the length of mm the minor chela, the width and height of both 50-1 chelae, and body weight (Table 1). On the con- trary, the length of the major chela differed sig- nificantly in its level of allometry in the sexes (Table 3), growing more rapidly in males (f=2.90. P<0.01). with no difference between 20- the growth rate for right- (over 90% of the entire 10- population; Gherardi et al., 1987) or left-handed individuals (/=0.076. df= 148. ns). The allometric growth of the major chela was not constant (Fig. 4 and Table 3): the slope of the 20 30 50 regression line increases at 15 and 35 mm CL in 15 35 males, and at 3.*^ mm in females. The ccdyses n=153 Q occurring at these sizes are assumed to corre- pond to the pre-puberty (otiiy shown in the males) and puberty moults, respectively, thus demarcating three phases; juvenile (CL <15 mm), when individuals are still sexually 20- > undifferentiated; sub-adult (CL ^\5 mm and • <35 mm), when sexual dimorphism becomes 10- apparent: and adult (CL 3:35 mm), when the animals attain sexual maturity. The abbrevia- tions J. SM. SF, AM and AF will be used in the I text to refer to juveniles, sub-adults and adults, I 20 30 I 50 15 35 males and females respectively. CARAPACE LENGTH mm The abdomen showed the most evident growth differences between the sexes (Fig. 5 and FIG. 4, Allometric growth of major claw length in Table 4). The female abdomen began to widen males (top) and females (bottom) versus carapace length. The discontinuities of the curve mark the pre- faster at 15 mm CL. its growth rate slowing puberlal (males, at \^ mm CL) and pubcrtal (males down after 35 mm. In males, a variation in slope and females, at 35 mm (CL) moults. Plotted on was seen at 15 mm, with no difference in the logarithmic scale. 496 F. Micheli, F. Gherardi and M. Vannini

TABLE 4. Growth rate of abdomen width (v. In of carapace length) in different instars (•/'<0.05: '•P<0.01) ln (abdomen width)

N b Juveniles (<15 mm) 27 1.126 0,90

Males Females f t N b (£.#1) N b Sub-adults (15-35 mm) 80 0,871 3.13' 90 2.058 20.18" 16.82" Adults (>35 mm) 148 0.951 1.05" 145 1.363 3.16" 3.54"

Males Females ( df t df Juv. V. Sub-ad. 2.02* 105 7.97" 115 Sub-ad. V. Ad. 1.13 226 5.66*' 233

mm 2). Gonopods of the first pair, which are = 497 positively ailometric in immature crabs of other z species (Hartnoll, 1974), were isometric in both O 20-1 S (r=1.317, df=2, ns) and A males (r=1.274, df=15, ns), and no change occurred at the Z 10-1 Ul puberty moult (S v. A: r=0.346, df=15, ns). Female pleopod exopodites (considering the I average length of the four pairs) grew faster, a relative to CL, in S (/=8.823, df=4, P<0.001) and isometrically in A (r=0.905, df=l3, ns), 10 15 30 35 50 with a significant difference between these two CARAPACE LENGTH mm categories (/=8.588.df= 13. P

aio4 30

g 1.0^

S

0.50-1 < o o 0.10- 0.05 30 45 mm

CARAPACE LENGTH FIG. 6. Correlation belween body size (carapace length) and gonad weight (wet) in males (top) and females (bottom).

df=4, P<0.02: AM: r=0.861. &=0.26, df=14. teen males (ranging from 25.4 to 50.5 mm CL) P<0.001;SM v. AM: r=2.706. df=14,/'<0.02; revealed the constant presence of sperms in ani- SF: r=0.724, 6=0.013, df=3, ns; AF: r=0.643. mals over 35 mm, while they were never found 6=0.088, df=13, P<0.01; SF v. AF: /=2.652, in S individuals. df=13, P<0.02). In S, gonad weight exhibited a slight positive allometry in males, while female ovaries were inconspicuous until the onset of Viteilogenesis sexual maturity. Weight increased rapidly in At the onset of viteilogenesis, the originally both sexes in the larger classes. white, thin ovaries acquire a creamy colour and Vas deferens. The anatomical subdivision pro- start to grow as a consequence of the deposition posed by various authors (Cronin, 1947; Ryan, of yolk inside the oocytes. As this process con- 1967; Hinsch & Walker. 1974} of vas deferens tinues, the ovary turns yellow in colour and. into anterior, medial and posterior portions was finally, bright orange. Oocytes on the external adopted. Classification was made on the basis of surface of the ovary started to colour at about the external appearance and position of the def- 0.5 mm diameter. This agrees with the classifica- erential tracts without histological examination. tion of vitellogenic stages proposed by Adiyodi The presence of sperms was checked in the ante- (1968). In our histological sections of ovaries, rior and medial regions. minute eosinophilic granules were present at the Examination of the vasa deferentia from six- periphery of the oocytes over 0.5 mm in dia- 498 F. Micheli. F. Gherardi and M. Vannini

100- -CARRViNG FEMALES n = 156

50-

0-" 20 15 22 30 7 13 21

AUGUST SEPTEMBER OCTOBER

100-I BROOD-CARRYING FEMALES n = 156

0 -

AUGUST SEPTEMBER OCTOBER FIG. 7. Time of spawning (lop) and hatching (bottom) (per cent of egg- and brood-carrying females, respectively, founded in transects along the stream from July to October),

meter and acidophily increased with cell size. and the first half of September. The distance Ovaries with oocytes larger than 0.5 mm on between the peaks of the diagram in Fig. 7 cor- average were thus considered as vitellogenic. responds to 1 month approximately but no direct All of the ten females measuring 26-35 mm measurement of the incubation period was CL examined had immature gonads, whilst only made. Pace et al. (1976) indicated a duration of one of the sixty-six adults (ranging from 35 mm 45±2 days at 23°C for this species in . All to 46 mm) had a non-vitellogenic ovary. breeding females found at stream inspections (26.4% of total number of females) were in the instar indicated here as A. and the size distribu- Functional sexual maturity tions of breeding and non-breeding individuals Oviposition and hatching. Egg-bearing females were found in the stream from late July TABLE 5. Size frequencies of breeding and non- to early August (Fig. 7). Uke all freshwater breeding females found along stream transects from crabs studied to date (Koba. 1936; Schneider, July to September 1986 1971; Minei, 1976; Yamaguchi & Takamatsu. No. of females 1980; Pillai. 1982), and as already reported for Size range this species (Mercanti, 1885; Pace, Harris &Jac- (CL, mm) Breeding Non-breeding carini. 1976), hatehing occurs in the pouch lim- <35 0 41 ited by the mother's abdomen. Brood-carrying 3=35 and <40 s 12 females were found in the second half of August •^40 20 25 Growth and reproduction in a freshwater crab 499 were significantly different (;f^=24.0, df=2, chilipeds with his, or with his first pereopods and /^<(1.(IO1; Table5). grasping her with his pereopods. Although on the basis of morphometrical and The most striking feature was the difference in anatomical analysis it could be inferred that ani- size between the partners, the females always mals are already sexually mature at about being smaller than the males (females: CL from 35 mm CL, no breeding female under 38 mm 29.7to42 mm, average 35.74±(1.87 mm; males: was ever found and larger ones were more com- CL from 41.2 to 50.5 mm, average mon (average CL of breeding females 45.37±0.76 mm), Size frequencies (Table 7) of 41.99±0.28mm, n=45). mating and non-mating animals (comparing data The number of hatchlings for each female, gathered over the same peHtxJ) were signifi- counted in seven different broods, ranged from cantly different in boih sexes (males: x^= 19.624, 55 to 157 (average 103.7). No correlation df=l. /'<0.001; females: ;^=12.794, df=2. seemed to exist between CL of these females and P<0.01), which suggests that the difference in the number of hatchlings (r=0.23. df =5, ns),i.e. size of mating males and females is not simply a fecundity does not seem to increase with size. reflection of the size composition of the The fecundity of twenty-four females was evalu- population. ated by classifying the numerical consistency of The mechanisms of sex-recognition are still unknown. In two matings observed in the lab- oratory (male CL: 47.9 and 45.7 mm; female TABLE 6. Female fecundity relative to size CL: 34.5 and 34,7 mm) the first phases showed Egg masses Size range all the signs of an aggressive interaction, with Ihe (CL. mm) Small Medium Large male grasping the female by thechelipeds. then, after a few minutes, turning her over with the aid 38^2 3 2 4 42-46 6 6 3 of his pereopods and pushing her under himself, at the .same time inserting his abdomen tmder his partner's. In both cases, mating lasted about 3 h. the egg masses in three categories, i.e. small, Minei (1976) gave a similar description of mating medium and large (Table 6). and this confirmed behaviour in the river crab Geotelphusa dehaani the previotis results (Fisher test: ns). White. Sex-ratio at birth (determined in 293 crablets) Seminal receptacles from eighteen females did not differ significantly from 1:1; 47.4% were examined histologically. Out of fourteen (x^=0.577, df= 1, ns) of the crablets were mate. animals with CL >35 mm, captured in all months of the year, only one had empty sper- mathecae. Two adult, post-moult ('soft') Mating females also had masses of sperms in their recep- Fourteen mating pairs were observed in tacles, indicating that sperms are kept over nature, from May to October. In all cases both ecdysis. Sperms were also present in one YF partners had hard integuments and were found (34 mm CL), while other three YFs had not yet free in the water, in the open; only in two cases copulated. were they found at a entrance. The part- ners remained motionless for a period varying Discussion from 30 min to 21 h. with their ventral surfaces in contact, the male holding the female's The analysis of the population structure (con-

TABLE 7. Size frequencies of mating and non-mating individuals during the breeding season (CL=carapace length) Males Females Size range (CL. mm) Mating Non-mating Mating Non-mating <35 0 32 4 33 >35 and <40 0 8 8 12 >40 and <45 4 19 2 34 >45 9 7 0 0 500 F. Micheli. F. Gherardi and M. Vannini ducted on the same population as the present reproductive activity. However, while a positive study; Gherardi et al.. 1987). showed that the relation between female size and number of eggs size classes were not equally represented in the spawned has been shown in many sexes, individuals over 40 and under 30 mm CL species (e.g. Pseudocalanus minutus KreJyer, more often being males, whereas females were McLaren, 1965; Heterozitts rotundifrons Milne represented more in the35-4U mm CL range. In Edwards, Jones, 1978; Homarus americanus other decapods too, especially brachyurans Milne Edwards, Aiken & Waddy, 1980; Eriphia (Adams. Edwards & Emberton., 1985), females smithi MacLcay. Vannini & Gherardi. 1988). are smaller than males, as a consequence of an this was not the case in P. fluviatile, though increase in the intermoult interval, e.g. in Cancer ovary weight does exhibit a positive allometry pagurus Linnaeus (Bennet, 1974) and in Pachy- with respect to body size. grapsus crassipes Randall (Hiatt, 1948). and/or An alternative hypothesis explaining the of a reduction of the growth rate (as in the case of smaller size of females could be their higher Cancer magister Dana. Cleaver, 1949). P. fluvia- mortality rate, caused by the high cost of egg tile does not exhibit any sexual difference in production (especially if compared to the low carapace growth rate, contrary to the freshwater cost of spermatogenesis; Pillay & Nair, 1971), crab Paratelphusa hydrodromus Herbst from and/or by the Intense vagility exhibited during India, where a differential growth rate between the pre-ovulatory period (Gherardi, Tarducci & sexes was detected during sexual maturity (Ku- Vannini, 1988), bringing exposure to risks of nip& Adiyodi, 1981). both and dehydration as a con- Though in most decapods the increment at sequence. The evidence that the sex-ratio calcu- moult declines with size, some exceptions do lated in this population (58.6% males) during exist, e.g. Carcinus maenas Linnaeus (Crothers, the winter months (i.e. in the period of the 1967; Hogarth, 1975). C. mediterraneus Czer- lowest vagility in both sexes), differs signifi- niavsky (Veillet, 1945), Maja squinado Herbst cantly from 50% (Gherardi et al., 1987), con- (Carlisle, 1957) and Pisa tetraodon Pennant trary to the sex-ratio at birth, could possibly (Vemet-Cornubert. 1958), All of these have a support the hypothesis of a higher mortality rate definite terminal anecdysis. which, however, amongst females. must be excluded in our case because large During the breeding season the sex-ratio females were also found, though only rarely (the changes, shifting in favour of the females in Sep- biggest animal found in the stream was in fact a tember, i.e. when they carry the brood under female measuring 51.9 mm CL). their abdomens, so that their locomotor activity A second possible mechanism limiting female is limited and they crowd into the stream size could be a lengthening of the moult interval (Gherardi et al., 1988a). A similar seasonal compared with males, caused by the onset of variation in sex-ratio has also been observed in reproductive activity, which, at least in Geotelphusa dehaani White (Yamaguchi & Anomura and Brachyura (Adiyodi, 1985). is Takamatsu, 1980). The lowering of moult fre- restricted to the intermoult period. Further- quency with the onset of sexual maturity (over more, both moulting and reproduction entail 35 mm CL) is not surprising, because the same considerable energy demands (Passano, 1960; phenomenon is widely observed in all Crust- Yamaguchi & Takamatsu, 1980; Adiyodi, 1985; acea, and is probably connected to the energy Gherardi, Tarducci & Micheli, 1989). Since, in cost of reproduction (Hartnoll, 1982). the populations of P. fluviatile Herbst in temper- The different distribution of moulting animals ate areas, the breeding and moulting seasons in the two sexes observed in smaller classes (in almost coincide, it is unlikely that an animal particular for CL >25 and <35 mm, where there would undergo both events in the same annual were more moulting females than males) indi- cycle. In terms of optimization strategies, the cates that females grow faster than males as they size range of mature females could represent a approach the puberty moult, anticipating the compromise between the advantages to be had onset of their reproductive activity. The from spawning every year, and from reaching a acceleration of moult frequency prior to sexual larger size before maturity, and thus higher maturity could explain the large number of adult fecundity (i.e. the number of eggs produced per females in the population (Gherardi ei ai, animal per breeding season) with the onset of 1987). The length and frequency of oogenic Growth and reproduction in a freshwater crab 50! cycles seem to be characteristic for each crusta- contrary, exopodites grow faster relative both to cean species in a given environment, because carapace and abdomen length prior to the oviposition is timed by some environmentally puberty moult, while they become isometric in correlated mechanism is such a way that it takes the adult phase. Female exopodites protect eggs place when conditions are likely to be favourable and brood, preventing them from loss and for the release of the young. For instance, in dehydration. Apositiveallometry of these struc- Paratelphusa hydrodromus Herbst, a freshwater tures before puberty would therefore grant an crab with a wide geographical distribution in adequate protective structure as soon as the India, oviposition occurs from March to October female is ready to spawn for the first time. Pro- in South Kerala, where rains are scattered, while tection of the brood is particularly important for in North Kerala, where rains are more seasonal. this species in relation to the long time the young it only occurs in March, so that release of the stay under the mother's abdomen and the risks young coincides with the beginning of the mon- arising from tbe environment (newly hatched soon. In the first case, multiple spawning over a crabs could be carried away by the current or single annual cycle seem to be the rule, while the become dehydrated). northern populations spawn once only No difference was observed between the sexes (Adiyodi, 1985). in the level of allometry of carapace width versus The patterns of relative growth by chelae, het- CL, which in many species is related to the ovary erochely, and abdomen follow those already development (Hines, 1982; Vannini & shown in most species studied so far (Hartnoll. Gherardi, 1988). However, in male /'. fluviatile, 1974), and the adaptive value of the allometry gonads are very voluminous, especially the def- exhibited by these organs has already been erens portion, ranging from 1.5% to 5% of the largely discussed (Hartnoll. 1974, 1982; Finney total body wet weight in adult animals, while in & Abeie, 1981; Vannini & Gherardi, 1988). the females gonad weight only exceptionally P. fluviatile males do not adhere to the exceeds 2% (Micheli, 1988). The considerable general branchyuran trend of positive allometry development of the male reproductive system in of the first pleopods versus carapace length in this species does not seem to be a general feature the instars preceding puberty, as their growth is of freshwater brachyurans: in the river crab isometric relative to carapace and abdomen Barytelphusa guerini Milne Edwards, for lengths in both S and A, According to Hartnol! example, female gonads are heavier than those (1974), allometric growth of male gonopods of males (Gangotri et al., 1978). brings them to an operative size at puberty. Both sexes of P. ftuviatile undergo the puberty Their growth is correlated witb the size of the moult at approximately the same size (35 mm genital openings of the females. Large male CL), but functional maturity (which in females gonopods would be disadvantageous, as they means the capability of producing eggs, and in would limit the size range of possible partners. males corresponds to the phase when they are In most species this is prevented by tbe negative first able to copulate; Hartnoll, 1969) is in both allometry exhibited by these structures in adult cases delayed, though to a different extent. The males(Hartnoll. 1974). However, in P.fluviatite long gap between the onset of sperm production mating is accomplished only by large males with and their effective transfer observed also in small females. This could justify the absence of a Portunussanguinolentus Herbst (Ryan, 1967) and positive allometry in the male gonopods, in the superfamily Oxyrhyncha (Hartnoll, 1963), because by the time a male begins its reproduc- might be adaptive either because larger males tive activity its gonofwds are probably already of have an advantage in agonistic encounters with the effective size with no need for accelerated conspecifics (Vannini. Gherardi & Pirillo, 1983). growth. or because large animals inspect wider areas and Allometry of female pleopods is a feature not meet more females; a positive correlation exists generally observed in brachyurans. Female between locomotor activity and body size (Gher- pleopod endopodites are slightly allometric rela- ardi etai, 1988a). tive to carapace length, but isometric with A deeper knowledge of reproductive abdomen length, which in turn is positively allo- behaviour, and sex-recognition mechanisms In metric with carapace length; endopodite growth partictilar, is of course necessary. In the case of could simply follow abdomen growth. On the females, mating is usually coincident or even 502 F. Micheli, F. Gherardi and M. Vannini precedent to the pubertal moult, so that sperms Cronin L.E. (1947) Anatomy and histology of the are kept in the seminal receptacles until ovula- male reproductive system of CalUnecies sapidus tion - all adult females had sperms in their sper- Rathburn. Journat of Morphotogy. 81, 209-239. Crothers, J.H. (1967) The biology of the shore crab mathecae. Storage of sj^erms occurs in many Carcinus maenas (1..)- Fietd Studies. 2, 407-434. crustacean species (Sastry, 1983). In Finney W.C, & Abele L G , (1981) AUometric vnri- Chionoccetes bairdi Rathbun, sperms stored in ation and sexual maturity in the obligate coral com- the receptacles are still viable after 2 years (Paul, mensal Trapezia ferruginea Latreille (Decapoda, 1984). In some cases, sperms received during a Xanthidae), Crustaceana, 4\, 113-130, Gangotri M.S,, Vasantha N. & Venkatachari S.A.T, single copulation may fertilize eggs for several (1978) Sexual maturity and breeding behaviour in ovipositions (Hartnoll, 1963; Ryan, 1967). the freshwater crab. Barytetphusa guerini Milne \x\ P.fluviatite, mating of pre-pubertal females Edwards. Proceedings of the Indian Academy of could be advantageous, due to the vagile and Science. 87B, 195-201. Gherardi F.. Guidi S. & Vannini M, (1987) largely terrestrial habits characterizing tbeir Behavioural of the freshwater crab adult phase, which reduce the possibility of Potamon Jtuviatile. preliminary observations. encountering males, and/or to the considerable Investigacion Pesquera. 12, 222-234. overlap of the mating and breeding season, so Gherardi F., Messana G.. Ugolini A. & Vannini M. (1988a) Smdies on the locomotor activity of the that, by the time mating does occur, most freshwater crab, Potamon fiuviatile. Hydro- females over 38 mm CL already carry a brood. biotogia, 169, 241-250. Gherardi F., Tarducci F. & Micheli F. (1989) Energy maximization and foraging strategies in Potamon Jtmiattle. Freshwater Biotogy, 22, 233-245. Acknowledgments Gherardi F,. Tarducci F, & Vannini M. (1988) Loco- motor activity in the freshwater crab Potamon ftuviatite: the analysis of temporal patterns by Many thanks are due to Dr Carlo Calloni for his radio-telemetry. 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