Rudolf Diesel

Rapid evolution to terrestrial life in Jamaican crabs

Crabs of the family Grapsidae are abundant organisms in most intertidal communities. However, relatively few species live in complete independence of the sea. Of those species that do, Jamaicas nine endemic species of land crabs are unique in their exceptional adaptations to terrestrial life, which include the only active brood-care for larvae and juveniles known in crabs. These adaptations, and the morphological similarity to a group of southeast Asian land-dwelling crabs, have raised the question of the number and age of land invasions of the Jamaican species. Here we present molecular evidence that Jamaican land crabs represent a single adaptive radiation from a marine ancestor that invaded terrestrial habitats only 4 million years (Myr) ago. A Late-Tertiary origin has also been found for lizards and frogs of Jamaica and probably reflects the Mid-Tertiary inundation of that island.

Parental care in an unusual environment: metopaulias depressus (Decapoda: Grapsidae), a crab that lives in epiphytic bromeliads

Abstract The adaptive value of parental care was studied in the Jamaican bromeliad crab Metopaulias depressus which passes its entire life-cycle in epiphytic bromeliads. For breeding, females choose large plants with above median water volumes. Larvae are released into a nursery axil water reservoir and pass through an abbreviated development (9–10 days). The young crabs remain in the nursery and are tended for about 8 weeks. Maternal care consists of three major behavioural components. (1) Females create a nursery by clearing a leaf axil of all leaf litter and organic debris except for snail shells, which are retained. These manipulations in the nursery may improve the dissolved oxygen and carbon dioxide balance of the axil water, and change the pH from acid to neutral. (2) Breeding females defend the young in the nursery against predators, mainly damselfly nymphs and spiders. (3) Mothers feed their young with prey (snails, millipedes) caught on the bromeliad and carried into the nursery. In a field experiment orphaned broods suffered significantly greater mortality, grew more slowly and gained less weight than mothered broods. Hence, parental care significantly benefits the females fitness by increasing offspring survival and growth. Delayed dispersal of young crabs results in the formation of family groups, consisting of a mother with her offspring from several different breeding seasons. Metopaulias depressus is the first decapod known to prepare a nest structure, to defend and feed its young and to live in family groups.

Maternal care in the bromeliad crab Metopaulias depressus (Decapoda) : maintaining oxygen, pH and calcium levels optimal for the larvae

SummaryHarsh physico-chemical conditions during early development may select for parental care. However, no study on the evolution of parental care has focused on the physico-chemical conditions in the environment, the physiological needs of early life stages and the significance of parental care. Early development of the bromeliad crab is completed in small rainwater reservoirs in bromeliad leaf axils. Axils not cared for by mother crabs are acidic, hypoxic and contain very little Ca2+. Maternal care buffers axil water and increases oxygen and Ca2+ availability. Our results show that (a) bromeliad crab larvae die at pH levels usually found in unattended axils, but develop successfully into the first crab stage at the pH typical of cared-for axils; (b) oxygen concentration in unattended axils is below the critical concentration for larvae, but is high enough for normal respiration in cared-for axils; (c) the calcium demand of larvae for moulting and development cannot be satisfied in unattended axils, but is met by the higher calcium content of cared-for axils. Therefore, physicochemical conditions in the bromeliad axil habitat exert strong selection for the maintenance of parental care in the bromeliad crab.

Effects of Salinity and Starvation on the Larval Development of Sesarma Curacaoense De Man, 1892, a Mangrove Crab with Abbreviated Development (Decapoda: Grapsidae)

ABSTRACT The ecology and development of the mangrove crab Sesarma cuaracoense was studied in Jamaica. Salinity and temperature were measured in the natural habitat of this crab, and the effects of various salinities, different temperatures, and starvation regimes were studied in the laboratory. The crab inhabits mangrove swamps where salinity and temperature ranged from 8-45 ppt and 22.2-39.0°C, respectively, and its larval stages were found in the mangrove area and in an offshore lagoon. Females produced relatively few (112-980) moderately sized eggs (mean diameter = 0.58 mm after spawning). Development was abbreviated and consisted of 2 swimming, morphologically advanced zoeal stages and 1 megalopa, and the first crab was reached after an average of 13.5-19.3 days when larvae were fed. Development to the first crab stage was completed at salinities ranging from 10-55 ppt. However, a high mortality appeared at the extremes of 10 and 55 ppt. When starved from hatching, yolk reserves were sufficient for development to the megalopa stage, during which food was required in order to molt to the first crab. Sesarma curacaoense had fewer larval stages, the larvae tolerated a wider range of salinities for development, and showed a higher degree of lecithotrophy than reported for other species of Sesarma outside Jamaica. Its mode of development is similar to that in the endemic Jamaican species (2 zoeae), and its degree of lecithotrophy is intermediate between its semiterrestrial and truly fresh-water and terrestrial relatives.

Maternal care in the bromeliad crab, Metopaulias depressus: protection of larvae from predation by damselfly nymphs

Metopaulias depressus (Decapoda, Grapsidae) is a crab that breeds in water-storing leaf axils of large Jamaican bromeliads. This study examined whether and how maternal care protects crab larvae from predation by damselfly nymphs. The nymph of the bromeliad-breeding damselfly, Diceratobasis macrogaster, is the major predator on bromeliad crab larvae. Laboratory tests revealed that a nymph kills on average five larvae per day. Both the damselfly and the bromeliad crabs prefer the bromeliad Aechmea paniculigera as a breeding site. Nymphs were abundant: 87% of the A. paniculigera held 1–16 nymphs. Bromeliad crabs release on average 50 larvae into a prepared nursery axil where they develop for 9–10 days into young crabs. In field experiments maternal care reduced larval mortality from predation by 60%. A calculation based on predator abundance and killing potential suggests that female brood desertion would lead to 54–100% loss of their reproductive investment, depending on the females body size and age (egg number is positively correlated with body size). Protected broods showed on average only 22% mortality during the larval period. In the bromeliad crab, predation on larvae exerts strong selection on the maintenance of maternal care for larvae.

Effects of Salinity and Starvation on Larval Development of the Crabs Armases Ricordi and A. Roberti (Decapoda: Grapsidae) from Jamaica, with Notes on the Biology and Ecology of Adults

ABSTRACT Adult ecology, egg production, larval development, salinity tolerance, and starvation resistance of the grapsid crabs Armases ricordi and A. roberti were studied in Jamaica. The species have different adult habitats. Armases ricordi lives in dry hot habitats up to 200 m from the shore, whereas A. roberti lives on the banks of fresh-water rivers up to 9.6 km from the sea, a relatively moist habitat with moderate temperature variations. Newly deposited eggs were significantly larger in A. roberti (0.40 mm) than in A. ricordi (0.35 mm). Both species produced many eggs per clutch, more than one clutch in an intermolt stage, and at least one clutch of eggs was fertilized without remating. Ovigerous females of A. ricordi migrate to the sea for larval release, whereas A. roberti apparently release the larvae into the river to be transported to the sea. In both species, larval development takes place in the sea and consists of 4 zoeal stages. Duration of larval development did not differ between A. ricordi (16.1 days) and A. roberti (16.9 days), but the megalopa stage in A. roberti (12.0 days) was longer than in A. ricordi (9.1 days). In both species, larvae depended on food intake in order to complete development, and the duration of survival in starved larvae varied significantly between hatches. Larvae of Armases roberti, hatched with a larger body size, showed a higher endotrophic potential and the first crab stage was larger than in A. ricordi. The range of salinity tolerated for development to the megalopa was 20-45 ppt in A. ricordi and 15-45 ppt in A. roberti. The species differed greatly in salinity tolerance in the first zoeal stage, with 100% of the larvae surviving fresh water only for 1 h in A. ricordi, but for 2.5 days in A. roberti, allowing the first zoea of the latter to be transported to the sea from distant inland habitats. The differences between A. roberti and A. ricordi in endotrophic potential, body size, and fresh-water tolerance of the first zoea are likely to be related to the larger egg size and, hence, larger yolk provisioning per egg in A. roberti. We discuss the significance of migration and larval release pattern in relation to inland distribution of adults for species with marine planktonic development.

Effects of Salinity, Temperature, and Starvation on the Larval Development of Armases (= Sesarma) Miersii (Rathbun, 1897), a Semiterrestrial Crab With Abbreviated Development (Decapoda: Grapsidae)

ABSTRACT The development of the Jamaican grapsid crab Armases miersii was studied in laboratory experiments under various conditions of salinity, temperature, and starvation. Females produced 908-4,334 medium-sized eggs (mean diameter = 0.51 mm). Development was abbreviated and consisted of 3 morphologically advanced zoeal stages and 1 megalopa. Development to the first crab stage took place in salinities ranging from 5-50 ppt. With increasing temperatures, duration of development decreased and survival at low salinities increased. These features enable the larvae to survive in a highly variable environment, supratidal rock pools along the coast of Jamaica. When continuously starved, energy reserves in larvae were sufficient for development through the first and occasionally the second zoeal stage, but later stages must feed in order to survive. Compared to other species of Armases, A. miersii produced fewer, larger eggs, larval development consisted of only 3 instead of 4 zoeal stages, larvae tolerated a wider range of salinities, and showed a higher degree of lecithotrophy. The abbreviated development and partial lecithotrophy are discussed as a step toward emanicpation from the marine environment.

Breeding in a rockpool: larvae of the semiterrestrial crab Armases [=Sesarma] miersii (Rathbun) (Decapoda: Grapsidae) develop in a highly variable environment

Abstract The sesarmid crab Armases miersii (Rathbun) undergoes development in supratidal rockpools. We studied the ecological conditions in these pools, the breeding behavior of females, and the larval development and behavior on the Jamaican north coast in spring and summer 1992 to 1994. Individually marked females showed a high site fidelity, visited, molted and released their larvae repeatedly in the same pools. Larvae occurred in rockpools throughout the study periods. An abundant microfauna as well as detritus in the pools provided food resources for developing larvae. Experiments with a predatory corixid bug, which sometimes populates rockpools, indicate that larval survival in pools is significantly threatened by these bugs. Diurnal variations in pools were highest for temperature, ranging on average from 24.4 to 32.7 °C, and for oxygen saturation ranging from 20 to 155%. The mean pH values varied moderately between pH 8.3 to 8.9 and the salinities remained constant. Seasonal salinity variations were influenced by seawater spray, evaporation, precipitation and the distance of pools from the shore. Mean salinities and the pattern of their variation differed greatly between pools. In pools near the shore, mean salinities in 1992 ranged from 31.5 to 36.1 ppt and salinity varied between 0 to 120 ppt. In one pool distant from the shore mean salinity was 2.7 ppt and salinity varied between 0 to 8 ppt. Average salinities in the same pools were significantly higher in 1992 than in 1993, because of higher precipitation in 1993. Stratification in salinity and temperature occurred after heavy rains. Stratification in oxygen saturations occurred every night with on average 26% in the surface layer and 20% or less below the surface. Exposed to oxygen saturations below 30% for several hours, larvae did not survive in laboratory experiments. We observed that larvae in pools aggregated in the surface layer at night, whereas they were dispersed in the water column and feeding during the day. The mean duration of development to the first-crab stage in three rockpools was 11.5, 13 and 16.3 days at a mean temperature of 27.6 °C and shorter than the 17.5 days at 25 °C in the laboratory. However, the high salinity fluctuations in the pools, caused higher larvae mortality than the stable conditions in the laboratory. This study shows that the development of A. miersii larvae in Jamaican supratidal rockpools is subjected to highly variable and unpredictable abiotic conditions and that food availability is generally high.

Morphological and molecular evidence for a new endemic freshwater crab, Sesarma ayatum sp. n., (Grapsidae, Sesarminae) from eastern Jamaica

Recent morphological studies have shown that the Jamaican mountain stream crab, Sesarma bidentatum Benedict, 1892 (Sensu Abele 1992), consists of several allopatric forms. Three new species have been described from western Jamaica (summarized in Reimer et al. 1998) restricting the range of S. bidentatum to central and eastern Jamaica. In this study we used morphology and genetic markers to further distinguish crab populations from different East Jamaican river systems. Morphological characters such as the shape of male gonopods, front, chelar carpus, and walking legs, as well as mtDNA sequence (16s rRNA gene) comparisons were consistent in the separation of populations of S. bidentatum into two distinct groups. A new species, Sesarma ayatum sp. n., is described with a distribution from easternmost Jamaica to the eastern Blue Mountains.

ABBREVIATED DEVELOPMENT OF ARMASES MIERSII (GRAPSIDAE: SESARMINAE), A CRAB THAT BREEDS IN SUPRALITTORAL ROCK POOLS

Armases miersii is the only crab known to complete larval development in supralittoral rock pools. This habitat is characterized by harsh and highly variable abiotic and biotic conditions, requiring ecophysiological and ontogenetic adaptations. In this study, the complete larval development of Armases miersii from laboratory-cultured and field-collected material from Jamaica is described. Development consists of 3 zoeal stages followed by a megalopal stage. It is thus abbreviated in comparison to other species of the genus Armases and the closely related Aratus pisonii, which have 4 zoeae and 1 megalopa. Morphology of the zoeal and megalopal stages is compared with those of other species of the genera Armases and Aratus for which larval development has been described. The reduction of zoeal stages is discussed in relation to its ecological and evolutionary