Bimodal Size-frequency Distributions Research Articles

First report of the order Mysida (Crustacea) in Antarctic marine ice caves, with description of a new species of Pseudomma and investigations on the taxonomy, morphology and life habits of Mysidetes species.

SCUBA diving explorations of three islands off Dumont d’Urville Station at the coast of Adélie Land, East Antarctica, enabled the observation of marine ice caves. Sampling in this unusual habitat yielded a total of three species of Mysidae, altogether previously poorly known or unknown to science. Pseudommakryotroglodytumsp. nov. is described, based on the structure of the antennal scale, telson and on cornea-like lateral portions set off against the main body of eyeplates. Mysidetesilligi is re-established at species level after almost a century in synonymy. Re-descriptions are provided for M.illigi and M.hanseni, based on types and ice cave materials. Keys to the Southern Ocean species of Pseudomma and to the world-wide species of Mysidetes are given.Phylogenetic trees are provided for the genera Pseudomma and Mysidetes. 18S rDNA sequences of P.kryotroglodytum differ from GenBank sequences of other Pseudomma species. First sequence data are given for species of the genus Mysidetes: 18S differs between the two examined species and COI is quite diverse between and within species.We found previously unknown, probably sensorial structures in these ice cave species: in P.kryotroglodytum, the basal segment of the antennula shows a pit-like depression with striated pad on the bottom and a median cyst, connected with the bottom of the eyeplate cleft. M.illigi shows a female homologue of the appendix masculina bearing a field of modified setae. Subsequent investigations demonstrated these structures also in species from other habitats.The feeding apparatus and stomach contents of the three ice cave species point to brushing of small particles (detritus, microalgae) from available surfaces, such as sediment, rock and the ice surface. Differences in the feeding apparatus are very subtle between the two Mysidetes species. The high content of fat bodies in M.hanseni could help it to survive periods of starvation. The large storage volume of the foregut in P.kryotroglodytum points to the collection of food with low nutritional quality and could help to balance strongly fluctuating food availability.Summer specimens of M.hanseni showed a bimodal frequency of developmental stages in the marsupium and bimodal size-frequency distribution of free-living stages. The females with younger brood (embryos) were, on average, larger and carried more marsupial young than those with older brood (nauplioid larvae). All examined incubating and spent females showed (almost) empty foreguts and empty ovarian tubes, suggesting possible semelparity and death following the release of young. The absence of juveniles and immature females from summer samples suggests that growth and accumulation of fat and yolk occur outside ice caves, while such caves could be used by fattened adults as shelter for brooding. A provisional interpretation proposes a biannual life cycle for M.hanseni, superimposed with shifted breeding schedules, the latter characterised by early breeding and late breeding females, probably in response to harsh physical and trophic conditions along the continental coast of Antarctica.

The ovarian development, fecundity and hypothesis on spawning pattern of common cuttlefish Sepia officinalis off Mauritania

Cephalopod species have evolved highly flexible spawning strategies, but the extent to which spawning strategy adopted is inextricably linked to the ovarian development. To address the spawning strategy of common cuttlefish Sepia officinalis outside northwest Africa, an analysis of ovarian development and hypothesis on spawning pattern was undertaken for specimens (mantle length of 126–270 mm from stages II to IV) collected from commercial catches off Mauritania during summer months of July and August 2015. It was found that the mature/spawning female S. officinalis covered a wide range of body size, being 148–270 mm ML, and showed non-stop food intake. The gonadosomatic index (GSI) increased steadily with maturity from 2.13% to 13.22%, being higher mean value of 8.65 ± 1.69% at mature/spawning stage. Potential fecundity (PF) increased with female size from 1306 to 3376 oocytes (mean 2327 ± 554.47). The oocytes were developing asynchronously as evidenced by the dominant small oocytes throughout sexual maturation and a bimodal size-frequency distribution of yolk oocytes for animals at maturing and mature/spawning stages. The mature oocytes in ovaries of mature/spawning individuals consistently accounted for less than 1% PF. There were about 770–1966 viable eggs that would be released during the spawning season. These evidences indicate that S. officinalis off Mauritania undergo the asynchronous ovarian development, and adopt a complementary spawning strategy falling somewhere along a continuum between intermittent and multiple spawning to adapt to the nutrient-rich Mauritanian upwelling system.

Body-size and growth-rate divergence among populations of threespine stickleback (Gasterosteus aculeatus) in Cook Inlet, Alaska, USA

Body size is one of the most perceptible traits of organisms and is an important fitness proxy in evolutionary studies. Oceanic threespine stickleback (Gasterosteus aculeatus L., 1758) have colonized and adapted to numerous freshwater habitats throughout the Holarctic since the most recent glacial retreat, giving us natural “replicates” of both convergent and divergent evolution. I observed considerable body-size variation among 22 threespine stickleback populations within a small region surrounding Cook Inlet, Alaska, USA. Larger bodied populations tended to have bimodal size-frequency distributions, whereas most smaller bodied populations had unimodal distributions. Bimodal distributions suggested the presence of at least two age classes within large-bodied populations. I used a Bayesian approach to infer mean size of presumed age-1 and age-2+ fish from bimodal size-frequency distributions; I found significant differences in size among populations within ages and sexes, suggesting significant divergence in growth rate among populations. I did not find significant correlations between growth rates (age-specific size) and geographic distances among populations, drainage affiliation, or distance to the sea. Thus, historical processes like isolation by distance, gene flow, or recent common ancestry did not explain differences in growth among populations, suggesting a role for local adaptation or phenotypic plasticity in size divergence.

Self-sustaining infrapopulation or colony? Redial clonal groups of Himasthla elongata (Mehlis, 1831) (Trematoda: Echinostomatidae) in Littorina littorea (Linnaeus) (Gastropoda: Littorinidae) do not support the concept of eusocial colonies in trematodes.

Trematode sporocysts and rediae reproduce by parthenogenesis, forming clonal groups in the molluscan host. It has recently become popular to consider these groups as eusocial colonies, with division of labour between rediae morphs: small 'soldiers' incapable of reproduction defend the colony, while large rediae reproduce. Alternatively, clonal groups can be considered as self-sustaining infrapopulations. We tested these two hypotheses in the light of new data on rediae of Himasthla elongata (Mehlis, 1831) from snails Littorina littorea (Linnaeus) concerning ultrastructure, growth character and composition of their groups. Clonal groups under study contained rediae of different age and maturity stages: small (young) rediae, rediae with early cercarial embryos, rediae with late embryonic cercariae, rediae with fully formed motile cercariae, rediae with redial embryos and degenerating rediae. Small rediae had a reproductive organ, the germinal mass, whereas most large rediae with developing cercariae did not, which contradicts the eusocialconcept. Overall distribution of rediae by size and by gut to body length ratio was bimodal, which agrees with the eusocial concept ('soldiers' and 'reproductives' as modal size classes). On closer inspection, however, the bimodal size-frequency distributions (SFD) turned out to be the sum of unimodal SFD of rediae at various stages of maturity. The overall bimodality was determined by the character of redial growth resulting in a relatively low occurrence of intermediate morphs and by the developmental arrest in young rediae. The facts that small rediae can attack other rediae and concentrate in the anterior parts of the mollusc can be explained by age-related feeding preferences and niche segregation. They are unlikely to be associated with the 'colony' defence against invaders. To sum up, clonal groups of H. elongata rediae in our study represented self-sustaining infrapopulations. We failed to find any arguments in favour of their eusocial organisation.

Population dynamics of the pea crab Austinixa aidae (Brachyura, Pinnotheridae): a symbiotic of the ghost shrimp Callichirus major (Thalassinidea, Callianassidae) from the southwestern Atlantic

The Pinnotheridae family is one of the most diverse and complex groups of brachyuran crabs, many of them symbionts of a wide variety of invertebrates. The present study describes the population dynamics of the pea crab Austinixa aidae (Righi, 1967), a symbiont associated with the burrows of the ghost shrimp Callichirus major (Say, 1818). Individuals (n = 588) were collected bimonthly from May, 2005 to September, 2006 along a sandy beach in the southwestern Atlantic, state of São Paulo, Brazil. Our data indicated that the population demography of A. aidae was characterized by a bimodal size-frequency distribution (between 2.0 and 4.0 mm and between 8.0 and 9.0 mm CW) that remained similar throughout the study period. Sex ratio does not differ significantly from 1:1 (p > 0.05), which confirms the pattern observed in other symbiontic pinnotherids. Density values (1.72 ± 1.34 ind. • ap.-1) are in agreement with those found for other species of the genus. The mean symbiosis incidence (75.6%) was one of the highest among species of the Pinnotheridae family, but it was the lowest among the three studied species of the genus. Recruitment pattern was annual, beginning in May and peaking in July, in both years, after the peak of ovigerous females in the population (from March to May). Our findings describe ecological and biological aspects of A. aidae similar to those of other species of this genus, even from different geographic localities.

Relationship between metabolism, sex and reproductive tactics in young Atlantic salmon ( Salmo salar L.)

Atlantic salmon can differ markedly in their growth and in the timing of reproductive maturation, leading to the dramatic contrast between the large anadromous adults and the diminutive mature male parr. This study examined the growth rates, anatomical and physiological characteristics of parr during the adoption of their discrete life histories to ascertain whether these properties can explain tactic choice. To minimise the impact of habitat differences upon these attributes, salmon were reared in the laboratory until 1.5 years of age, when the “decisions” to undergo smoltification or to mature as parr had been taken. At 1.5 years, both males and females showed bimodal size-frequency distributions. Neither the population of origin nor the paternal reproductive tactic influenced the “decision” to mature or the growth trajectories. Growth rate (% mass day − 1 during their final 10 months) and the % male and female offspring in the upper modal group were strongly correlated and varied markedly among families. Mean growth rate per family was negatively correlated with mean metabolic rate per family at emergence. Growth rate decreased as a function of parr size in January and the growth rates of upper modal fish were displaced upwards relative to those of lower modal fish. Most males in the smaller size mode matured, whereas all other fish began smoltification. Mature male parr did not differ from similarly sized female pre-smolt in routine metabolic rate, but these smaller fish had higher metabolic rates than larger male and female pre-smolts. However, mature parr differed markedly from similarly sized females and from larger male and female pre-smolts in possessing higher oxidative and lower glycolytic capacities in muscle. Overall, these data are consistent with the interpretation that growth rates dictate the distribution of parr between upper and lower modal groups. Individuals from faster growing families would be more likely to pass the threshold for smoltification and to accelerate growth, whereas those from slower growing families would remain in the lower mode. The use of metabolic capacities, e.g. metabolic rate, was linked with modal group, whereas muscle oxidative capacity was linked with male maturity. Mean family metabolic rate at emergence was negatively linked with mean growth during the subsequent year, suggesting that metabolic efficiency facilitates growth and eventually smoltification.

Reproductive characteristics of Spondyliosoma cantharus (Linnaeus, 1758) in the Gulf of Tunis

Summary The reproductive features of Spondyliosoma cantharus were studied in the Gulf of Tunis to contribute to better fisheries management on a regional scale and to broaden knowledge on whether there are actual performance differences compared to others areas. A total of 369 fish were caught by trammel and gill nets in the Gulf of Tunis from January 2005 to June 2006. Sex-ratio, gonad maturation, size and age at maturity, sexual cycle, condition and reproductive strategy were determined. The male : female ratio was initially skewed in favour of females, with males predominating in larger sizes. Length of females at first maturity was 17.8 cm TL (n = 141), which corresponds to 4 years of age. A recommendation is made to increase the length at capture. Spawning season extends from January to May, with a peak in March–April correlated to the lowest sea surface temperatures (14.8–15.6°C); during this period, a dichromatism arises between males and females. The hepatosomatic index and the condition factor present significant monthly changes in relation to the breeding activity. The bimodal size frequency distribution, the biased sex ratio, and the presence of bisexual gonads outline a protogynous hermaphroditism; diandry should be confirmed.

The Systematics of a New Upper Ordovician Edrioasteroid Pavement from Northern Kentucky

A large, edrioasteroid-bearing hardground surface from the base of the Bellevue Member of the Grant Lake Formation near Maysville, Mason County, Kentucky is described. Four species are represented includingStreptaster vorticellatus(Hall),Carneyella ulrichiBassler and Shideler,Carneyella pilea(Hall), andCurvitriordo steckin. sp. Specimens ofS. vorticellatusandC. pileaadd little to the known morphologies of these species. However, prior to this studyC. ulrichiwas known from the unique holotype, andCurvitriordo steckin. sp. adds greatly to out understanding ofCurvitriordowhich was previously known from two species comprising three poorly preserved specimens.Curvitriordo steckishows a bimodal size frequency distribution suggesting seasonal breeding whereasCarneyella ulrichishows a left skewed size frequency suggesting low juvenile mortality.Streptaster vorticellatusshows a tight unimodal size frequency distribution suggestive of a single spat fall accumulation.

Allometry and population structure of Nicolea uspiana (Polychaeta: Terebellidae)

The relative growth and population structure of the terebellid Nicolea uspiana were investigated in the intertidal zone of a rocky shore on the south-east coast of Brazil, from May 2006 to May 2007. Eight hundred and forty-seven individuals of N. uspiana were analysed: 391 males, 163 females, and 293 immatures. Although significant differences in some morphometric parameters were found, there was no sexual dimorphism between males and females. There were differences in total length, width of segment 5, and length of the notopodial region between matures and immatures. The negative allometry of the total length in relation to five other parameters showed that this feature is a good measure for estimating the individual size, which was then used in the analysis of population structure. This population of N. uspiana showed a bimodal size–frequency distribution, with immature and mature individuals found during the entire year. This pattern indicates continuous reproduction, with each cohort growing for at least three to four months and being responsible for two consecutive settlement peaks.

Allometric dimorphism in the larvae of the salamander Hynobius retardatus

Hynobius retardatus has a head-width plasticity that is functional in cannibalism and preying on large creatures. Cannibalistic specialization in H. retardatus appears to a lesser degree than in those species that have clearly dimorphic morphs. To examine the degree of cannibalistic specialization and intraspecific phenotypic variation, we investigated the allometric relationship between the head and body in the larvae of H. retardatus in a single pond. In addition, the effect of cannibalism on the determination of morphology was examined. A field survey revealed the existence of allometric dimorphism and the occurrence of large-headed large larvae. However, we did not observe a bimodal size distribution that indicates a split in the population. A laboratory experiment revealed that the development of such large-headed large larvae was inducible by actual cannibalism and/or additional tactile cues under high-density conditions. We deduce that the allometric dimorphism in the larvae of H. retardatus in the wild is caused by actual cannibalism. The cannibalistic phenotypic variation in H. retardatus would be characterized by allometric dimorphism without a bimodal size-frequency distribution.

Population and reproductive biology of the fiddler crab Uca thayeri Rathbun, 1900 (Crustacea: Ocypodidae) in a tropical mangrove from Northeast Brazil

Abstract Population and reproductive biology of Uca thayeri Rathbun, 1900 were studied for the first time in a tropical mangrove. Absolute density, sex ratio, population structure, handedness, breeding season and fecundity were investigated. Seven transects were delimited in a mangrove area of the Pacoti River, Northeast of Brazil (3° 43′ 02″ S/38° 32′ 35″ W). On each transect, ten 0.25 m2 squares were sampled on a monthly basis during low tide periods from September 2003 to August 2004. A total of 483 crabs were obtained, of which 250 were males, 219 non-ovigerous females, and 14 ovigerous females. The U. thayeri population presented bi-modal size frequency distribution, with males and non-ovigerous females not differing significantly size-wise. Ovigerous females were larger than males and non-ovigerous females. The overall sex ratio (1:1.07) did not differ significantly from the expected 1:1 proportion. The major cheliped was the right one in 50% of the males. The observed density was of 8.5 individuals/m2, with the specimens being found mostly in shaded areas. Ovigerous females were found in 5 months of the year, coinciding with the rainy season, suggesting that the population of U. thayeri presents seasonal reproductive events. Juvenile crabs were more abundant during the dry period, while larger crabs were found mainly during the rainy period. The fecundity of the studied population was much smaller than that of subtropical populations of this species. The regression analysis shows that the number of eggs increases linearly with the increase of carapace width.

REPRODUCTIVE STRATEGIES OF TWO SYMPATRIC 'SMALL BARBS' (BARBUS HUMILIS AND B. TANAPELAGIUS, CYPRINIDAE) IN LAKE TANA, ETHIOPIA

The reproductive strategies of two species of 'small barbs' ( 12,000 fish). Both species have a long breeding period (from March to September), and the distinct bimodal size-frequency distributions of eggs suggest multiple spawning for both species. Absolute fecundity increased exponentially with fish size, and was significantly higher for B. humilis than for B. tanapelagius. Egg size was similar. Relative fecundity was significantly higher in B. humilis. In most habitats B. tanapelagius reached first maturity at a smaller size (58.5 mm) than B. humilis (64.5 mm). However, in shallow habitats with clear water B. humilis females are much smaller at first maturity (48.3 mm), possibly due to high tapeworm infection rates. The range of fecundity in small barbs from Lake Tana (172-339 eggs per gram) was low compared with small lacustrine cyprinids and clupeids from other African lakes. The reproductive strategies of the two barbs were discussed in relation to their feeding potential, food availability, parasite infection rate and risk of predation.

SYMPATRIC GROWTH MORPHS AND SIZE BIMODALITY IN THE GREEN SEA URCHIN (STRONGYLOCENTROTUS DROEBACHIENSIS)

Green sea urchins (Strongylocentrotus droebachiensis) have been a dominant structuring force in boreal, hard-bottom communities and recently have become an important fishery. Despite these roles, relatively little is known about the age, growth, and demographics of field populations. To begin to address these issues, we systematically sampled urchins during 1997 and 1998 at two sites (Allen Island [AI] and Schoodic Peninsula [SP]) in the Gulf of Maine, USA. Basic demographic information (density and size structure) was obtained and a subset of urchins aged by counting annual bands on the interambulacral plates. Size-at-age analyses showed that the population at AI consisted of two sympatric growth morphs, fast growing (fg) and slow growing (sg), each described by its own von Bertalanffy growth parameters for mean size and size variance. The two morphs also differed in maximum observed ages (sg, 6–11 yr, vs. fg, 16–18 yr) and in maximum test diameter sizes (sg, 30–35 mm, vs. fg, 50–70 mm). At SP, a single (fg) morph was identified which had growth characteristics similar to the fg morph at AI. An obviously bimodal size-frequency distribution at AI reflects the accumulation of urchins of each morph at asymptotic size. We advanced several hypotheses; including intrinsic factors, e.g., sex ratios, morphology, and genetics; and extrinsic factors, e.g., density, spatial distribution, settlement history, growth history, and migration; to explain the origin and coexistence of the two growth forms. Using primary and post hoc data analyses, we rejected sex ratio, density, spatial relations, and morphology. Analysis of annual growth and age structure indicated that the two morphs had different settlement histories, suggesting the mixing of two genetically distinct populations. Our post hoc analyses could not reject the genetics or growth history and migration hypotheses. Genetically different larvae, or else a phased process of differential settlement, migration, and growth (threshold migration hypothesis) are the most likely cause(s) for the two morphs. Our data indicate that field growth rates in green urchins are intrinsically highly variable, but also vary interannually probably in relation to their environment. Intrinsic variability provides a novel explanation for bimodality of size-frequency distributions in urchin populations. Interestingly, the sublegal size (<50 mm) and short life span of the sg morph preempts its recruitment into the fishery. Moreover, if the sg morph is widespread and genetically based, intensive harvesting may enhance selection for the sg morph. These findings may have serious implications for understanding the population structure and managing the green urchin fishery, and for assessing the grazing impact of these urchins in nearshore communities.

Behaviour and population structure of soldier crabsMictyris longicarpus (Latreille): Observations from a tidal flat in tropical North Queensland, Australia

Crabs of the family Mictyridae are common on sandflats of the Indo-West-Pacific. Activity patterns and population structure ofMictyris longicarpus (Latreille) were monitored in the Haughton River estuary in northeast Australia. The emergence of the crabs at low tide was intermittent and could not be related to lunar cycles, but the crabs were significantly more active on sunny than on rainy or overcast days. Of a total of 1494 crabs measured over a 14 months period, nearly 2/3 were males (951 crabs). No ovigerous females were found on the sandflat surface. Crabs active on the sediment surface ranged in size from 4.7 to 19.7 mm carapace length (CL). Distinct size-frequency distributions were identified for juveniles, females and males. The mean size of juveniles was 7.3 mm and of females 11.2 mm CL. Males showed a bimodal size-frequency distribution. The first mode (mean 8.5 mm) was clearly separated in size from the second mode (mean 15 mm). The population structure remained almost constant throughout the year. Juvenile and adult crabs showed different aggregation patterns and preferred different sediment types.

The population structure of the brittle star Ophiura sarsi Lütken in the Gulf of Maine and its trophic relationship to American plaice ( Hippoglossoides platessoides Fabricius)

This study examines the population structure of the ophiuroid Ophiura sarsi Lütken in an area southeast of Portland, Maine and its exploitation by its major predator, the flatfish, American plaice ( Hippoglossoides platessoides Fabricius). Ophiura sarsi and American plaice were sampled during a 1-yr period (1985–1986) from a site of 148–156 m depth. The bimodal size-frequency distributions of the O. sarsi population were dominated by small individuals with disk diameters between 2 and 11 mm, and with estimated growth rates, based upon the modal progressions from the persistent 1985 year class, of ≈4 mm per year. Larger individuals (≈15–25 mm) were generally less numerous. These older brittle stars, which formed the right-hand peaks of the size-frequency distributions, displayed little noticeable growth, which suggests that these peaks were comprised of multiple cohorts. Recruitment to the population appeared to be continuous, due to the occurrence of 1 mm or smaller brittle stars throughout most of the year. The strong presence of 1 mm or smaller O. sarsi in January, 1986 indicated a major recruitment event. A survey of the reproductive condition of the gonads showed evidence of continuous but seasonally variable reproduction, with the major spawning centered around January. O. sarsi was the major dietary constituent of the American plaice, occurring in at least 65% of the fish stomachs throughout the year. Plaice consumed the most abundant size classes of O. sarsi in the population, with disk sizes between ≈4 and 10 mm. These brittle stars were of low caloric value, yet the more nutritious, older brittle stars were not eaten in significant numbers by even the largest plaice. The high proportion of small, energy-poor O. sarsi found in the plaices' diet might be the result of their greater abundance or accessibility at this site.

The ovarian cycle in the natterjack toad, Bufo calamita, and its relation to breeding behaviour

Abstract The ovarian cycle in natterjack toads Bufo calamita from an island population with unpredictable breeding conditions was studied in an archipelago off the Swedish west coast. About 80% of the female population bred during spring and early summer, and the rest later in summer and early autumn. Time of breeding and female size (age) were not correlated. It was found that first growth phase (FGP) oocytes were recruited from oogonia mainly during early spring and late autumn, but that recruitment could occur at any time of the year. The FGP oocytes grew rapidly immediately after recruitment, and when transferred into second growth phase (SGP) oocytes. In between these two periods the FGP oocytes seemed to be in a resting stage. Females showed an asynchrony in ovarian developed. We found females with fully developed SGP oocytes, ready for ovulation, as well as females with ovaries in only an early vitellogenic growth phase at all times of the year. Females did not neccessarily ovulate as soon as the vitellogenic oocytes had reached full size. There were strong indications that some females only ovulated and laid a fraction of the egg mass in their first batch, and that they laid a second batch later in the season. This second batch was thought to originate from the same recruitment of oocytes as the first batch. There was a tendency for SGP oocytes to grow faster during summer than during spring. It was also concluded that SGP oocytes coulde be recruited all year around. Bimodal size frequency distribution patterns were found both among the FGP and the SGP oocytes; they were most pronounced among the latter, where they were found throughout the year.

Feeding Intensity, Growth Rates, and the Establishment of Life-History Patterns in Juvenile Atlantic Salmon Salmo salar

SUMMARY (1) Under good growing conditions, populations of juvenile Atlantic salmon develop a bimodal size-frequency distribution by late autumn of their first year; the larger fish in the upper modal group (UMG) will metamorphose into the sea-going phase the following spring, a year ahead of fish in the lower modal group (LMG). The feeding behaviour and growth rates of individually-marked fish from a sibling laboratory population were studied during the period when these two distinct life-history patterns become apparent. (2) The length-frequency distribution of the laboratory population was unimodal in August, significantly skewed by September, and clearly bimodal by December. Bimodality was a result of fish which joined the UMG putting on a brief growth spurt in late September/early October, at a time when water temperatures were falling and growth rates of LMG fish were decreasing. (3) Studies of the feeding behaviour of single fish in laboratory flume tanks revealed that the growth rate changes could be linked to changes in appetite rather than any external factors. The appetites of the two types of fish were initially similar in August, but then diverged: UMG fish showed a marked increase in appetite through to October, whereas the appetite of LMG fish decreased, with a small peak in October. (4) The results indicate that the fast and slow developing life-history patterns become fixed prior to September of the first year, and the corresponding changes in appetite and growth rate are thereafter under internal control. The October peak in appetite does not appear to be related to natural food availability, and may instead allow fish to obtain nutritional reserves prior to the winter when feeding is constrained.

Criteria for the Diagnosis of Hermaphroditism in Fishes

hermaphroditism can be diagnosed by the presence, within one gonad, of mature tissue of both genders or by experimental induction of self-fertilization. In sequential hermaphroditism (protogyny and protandry), convincing diagnoses will generally require the use of several indicative features. Features strongly indicative of protogyny are: membrane-lined central cavities in testes; transitional individuals; atretic bodies in stages 1, 2, or 3 of oocytic atresia within testes and sperm sinuses in the gonadal wall. The strongest indicators of protandry are transitional individuals whose gonads contain degenerating testicular tissue and developing ovarian tissue. Experimental production of transitional or sex-reversed individuals through manipulation of the social system may identify both protogyny and protandry. Because most indicators may be produced by more than one means, including sequential hermaphroditism, efforts should always be made to exclude alternative explanations for each piece of evidence. Features of population structure, such as bimodal size-frequency distributions with males a different size from females, or sex ratios differing from unity, are not reliable indicators of sexual pattern. Bimodal age-frequency distributions have fewer problems associated with their interpretation than do bimodal sizefrequency distributions.

REPRODUCTIVE BIOLOGY AND POPULATION STRUCTURE OF THE FIDDLER CRABUCA SUBCYLINDRICA(STIMPSON)

Comparatively large ova, low fecundity and low per capita egg production are adaptations to terrestrial habits in Uca subcylindrica. An unusual morphology of the genitalia appears to have co-evolved with the necessity for a lecithotrophic egg. Isolated populations are apparently sustained by rapid larval development. The crab stage population has a bimodal size-frequency distribution with an intermediate sex ratio pattern. Initially the sexes are equal, but males are more common in the larger size classes. Survival into the crab stage is relatively low. There is an increased rate of mortality with size. Only 30% of the individuals grow to modal carapace size; even fewer appear to participate in reproduction.

Spiny lobsters and sea urchins: Analysis of a predator-prey interaction

Spiny lobsters, Panulirus interruptus (Randall), are important predators of two species of sea urchins, Strongylocentrotus franciscanus (A. Agassiz) and S. purpuratus (Stimpson), which are major herbivores in southern California kelp forest communities. Aquarium experiments indicate that spiny lobsters strongly prefer S. purpuratus over S. franciscanus of comparable test diameter, probably accounting for the higher number of S. purpuratus mortalities observed in the field. Juvenile S. franciscanus (< 60 mm test diameter, TD) are preferred over larger conspecifics, but the smallest S. franciscanus (< 30 mm TD) are protected by association with the adult urchin spine canopy. Mid-sized S. franciscanus too large to fit under the spine canopy are subject to intense predation. All sizes of P. interruptus tested showed a notable reluctance to attack large S. franciscanus (> 90 mm TD) when offered a range of sizes, although the larger lobsters are capable of handling the largest urchins. Relative movement, spine length, test thickness, and gonad weights of sea urchins were examined to evaluate the factors affecting the lobsters' choice of prey, and behavioral responses to lobsters were assessed to determine urchin availability to these predators. The handling problems associated with the long spines of larger S. franciscanus appear to be the major considerations in prey choice despite the much greater potential energy gain from these urchins. Thus predation by spiny lobsters appears to be sufficient to explain the bimodal size-frequency distribution typical of S. franciscanus populations in areas where these predators are common. Heavy fishing pressure on spiny lobsters during this century probably resulted in the release of sea urchin populations and contributed to episodes of destructive urchin grazing observed in the 1950's and subsequent years.