The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life-history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean-type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico-chemical factors and phytoplankton availability in freshwater habitats. These life-history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r- to K-strategy in freshwater decapods are traded-off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio-temporal alteration of their socio-ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs.

Abbreviation of larval development and extension of brood care as key features of the evolution of freshwater Decapoda

Egg and clutch sizes of the fresh-water prawn Macrobrachium nipponense (de Haan) varied remarkably among local populations, corresponding to the hydrogeographic features of their habitats; spawning of many small eggs (approximately 0.05 mm3 in volume per egg) in a single clutch at river mouths, a few but large eggs (approximately 0.1 mm3) in inland fresh waters, and a moderate number of intermediate-sized eggs in brackish-water lagoons. The weight of egg mass deposited in one spawning also varied among populations from 15.6-24.3% in dry weight ratio to the female body weight. This change seemed to come largely from temporary environmental factors. Accordingly, the variation of clutch size among populations was partly due to temporary environmental factors, and partly due to the difference in egg size. This species is considered to be splitting into local populations with distinct reproductive traits through reproductive isolation in patchily distributed inland waters. Adaptive significance of varied egg and clutch sizes is discussed with emphasis on the role of larval dispersal.

Diversified egg and clutch sizes among local populations of the fresh-water prawn macrobrachium nipponense (de haan)

The reproductive biology of the Taiwanese fresh-water crab Candidiopotamon rathbunae (de Man) was investigated. The maturity, gonad development, mating behavior, breeding season, timing of release of young crabs, fecundity, and behavior of ovigerous females were studied. Mature males have sperm available for mating throughout the year. The deposition of yolk in females takes place mostly from April to June, with most of the eggs reaching maturity at the end of June. The main breeding season is from late June to October, although mating can occur all year round. In C. rathbunae, discernible courtship behavior is absent and a forced copulation strategy is practiced by males. Ovigerous females leave streams to live on the forest floor several meters away from the stream and are difficult to locate along the banks of streams. Ovigerous females return to the stream a few hours before hatching of the eggs. Most young crabs are released after mid-September, which is the end of the rainy season. This is ...

https://www.jstor.org/stable/pdfplus/1549167.pdf

Reproduction in the fresh-water crab candidiopotamon rathbunae (brachyura: potamidae) in taiwan

The external egg morphology of the phyllopod species recorded in France is described by means of S.E.M. Differences in diameter and ornamentation of envelope are stressed. We propose a dichotomous key to allow the identification of species even when their biotope is dry. Results are compared with previous studies on Anostraca, Notostraca and Spinicaudata and their taxonomical value is discussed.

Resting eggs of Anostraca, Notostraca and Spinicaudata (Crustacea, Branchiopoda) occurring in France: identification and taxonomical value

Summary

1. Freshwater crabs appear to show at least two alternative life history patterns, which differ in the timing of seasonal reproduction. Reproduction occurs during low flow among temperate lotic species, but during high water levels among wetland species. Crab biomass is often very high and both strategies would lead to spatial and temporal pulses in density and biomass. The life history and reproductive strategy adopted by tropical lotic species is poorly known, however, despite their importance in community and ecosystem dynamics.



2. In this study, we determined annual patterns of life history, density and biomass of a lotic freshwater crab in a small headwater stream in the East African highlands where it maintains high biomass. This crab is an as yet undescribed species of Potamonautes, here referred to as the Chinga crab.



3. Crabs were sampled non-destructively for 15 months using baited traps and benthic sampling with a Surber sampler. At the end of the study, an intensive hand search was carried out. Each method was biased towards different size classes of crabs and the efficiency of both long-term methods varied according to water levels in the stream. The intensive search was more effective than benthic sampling, but failed to record the large individuals caught by baited traps.



4. Population density and biomass remained constantly high throughout the study period. Reproduction, as evidenced by the presence of ovigerous females and small free-living juveniles, also showed no seasonality. As a consequence, the population size structure (size-frequency distribution) of crabs remained constant throughout the year.



5. The Chinga crab illustrates a third life history pattern, with no clear breeding season, and this may be common among tropical species. This is probably a consequence of the non-seasonal nature of its habitat: temperature varied little throughout the year and rainfall fluctuations were relatively small. This strategy allows the species to maintain high biomass without seasonal pulses and, perhaps, to dominate community and ecosystem processes.

Aseasonality in the abundance and life history of an ecologically dominant freshwater crab in the Rift Valley, Kenya

The reproductive cycle of the field crab Paratelphusa hydrodromous (Herbst) was determined by direct field observations as well as by calculating the percentage of ovigerous females in a Madras population for a period of three years. The females breed annually in a single spawning. These observations, corroborated by histological studies on the nature of the ovary, indicate that gametogenic activity starts in December and vitellogenesis is completed during January-May. Spawning commences in the last week of June or first week of July with the release of brood in the month of September (1979), October (1978) or November (1980) during northeast monsoon. The smallest female crab showing spawning had a carapace width of 3.1 cm and the largest spawning crabs measured 5.5 mm. The mean number of eggs spawned in the smallest crab was 247 and that in the largest crab was 417. Mean incubation was 41 ± 12.388 days. Vitellogenesis and spawning occurred at peak temperature conditions. Though the time taken for vitellogenesis and commencement of spawning were constant for the study period, the duration of retention of the juveniles in the brood varied with the onset of monsoon.

Monsoon-dependent breeding in the field crab Paratelphusa hydrodromous (Herbst)

The origin, ultrastructure and histochemical properties of the egg membranes in the South Indian anostracan, Streptocephalus dichotomus have been studied. The egg morphology and the ultrastructure of the tertiary membrane of this phyllopod crustacean have been examined both by scanning and transmission electron microscopy. Scanning electron microscopic observations on the egg surface reveal the characteristic ridges on the egg surface with pores. Similarly, the tertiary egg shell of S. dichotomus consists of two distinct layers, an outer cortex and an inner alveolar layer. There are specific differences in the structure and in the relationship of one layer to the other. The alveolar layer is characterised by large lipid droplets and an alveolar mesh. These two layers termed as tertiary layers are secreted by maternal shell glands. The outer tertiary egg layers are phenolically tanned, the precursor materials for tanning being derived from shell gland secretions.

Egg envelopes of Streptocephalus dichotomus Baird: A structural and histochemical study

Biochemical fluctuations during egg development of a field crab Paratelphusa hydrodromous (Herbst) have been determined and the values calculated on a per egg basis. Water content increases significantly initially and then drops to increase again in the last stage after hatching. There is a steady depletion of carbohydrate and lipid, but protein shows a steady increase. Nonprotein nitrogen shows an initial increase but declines drastically in the subsequent stages. The calorific content of different stages has been determined using a semibomb calorimeter. In general, a steady decline in the calorific content parallels the changes in the values of carbohydrate and lipid. Of the various yolk components spent during embryonic development, over 92% is lipid. Qualitative changes in the protein and lipid have been analyzed employing polyacrylamide gel electrophoresis and TLC, respectively. Accumulation of metals like Mg, Cu, Co, Fe, Zn, and Mn has been analyzed using an atomic absorption spectrophotometer at ea...

Yolk Utilization as an Adaptive Strategy of Terrestrialization in the Freshwater Crab Paratelphusa hydrodromous (Herbst)

Ootaxonomic findings on anostracan eggs: a scanning electron microscopic study

The protein pattern of haemolymph and body tissues of the freshwater fairy shrimp Streptocephalus dichotomus has been investigated in both sexes, using polyacrylamide disc gel electrophoresis. The electropherograms of four developmental stages show variations in number and intensities of protein fractions. In Stage III, two female-specific proteins of glycolipoprotein nature appear. This stage corresponds to maturity: females begin to possess mature oocytes in the ovary. These two vitellogenic proteins are well represented in the female haemolymph, ovary and freshly laid eggs, but are absent in the male haemolymph. A heterosynthetic mode of yolk formation is thus evident in this anostracan. The two sex-limited proteins are only faintly represented in shelled eggs, suggesting an early utilization of these compounds in embryogenesis.

T. Subramoniam

Papers

Monsoon-dependent breeding in the field crab Paratelphusa hydrodromous (Herbst)

Egg envelopes of Streptocephalus dichotomus Baird: A structural and histochemical study

Yolk Utilization as an Adaptive Strategy of Terrestrialization in the Freshwater Crab Paratelphusa hydrodromous (Herbst)

Ootaxonomic findings on anostracan eggs: a scanning electron microscopic study

Sexual and developmental differences in the protein pattern of haemolymph and body tissues of Streptocephalus dichotomus Baird (Crustacea: Anostraca)