Kristina von Rintelen

Evolutionary relationships of atyid shrimps imply both ancient Caribbean radiations and common marine dispersals

Abstract The evolutionary relationships of the surface genera of shrimps of the family Atyidae from the Caribbean were inferred using mitochondrial 16S ribosomal DNA and cytochrome oxidase I gene sequences. The genetic divergence among the 4 Caribbean genera (Atya, Jonga, Micratya, Potimirim) is extensive and dates from between the Eocene and Miocene. This result suggests a vicariant origin or the ancient dispersal of some taxa. Most intrageneric divergences date to the late Miocene–Pliocene and, thus, are probably the result of dispersal. Some species show low levels of intraspecific genetic divergence between distant islands, and thus, present-day or geologically recent gene flow is likely. This gene flow is probably a consequence of the amphidromous life histories of most Caribbean freshwater shrimps. Despite the ancient divergences between the genera, the Caribbean surface atyids form a single evolutionary lineage when compared with atyid shrimp from throughout the world, and this result implies an ancient evolutionary radiation in the Caribbean. The sister group to the Caribbean atyids are the large-bodied and robust Atya-like shrimps of the Indo-Pacific, which share a similar size and shape with Caribbean Atya. Thus, the common ancestor probably was also large and robust. In contrast, the other Caribbean atyids are much smaller, and Jonga has a distinct morphology that is associated with a switch from lotic to lentic environments. This radiation may have been the result of the absence from the Caribbean of other small shrimps that are common in the Indo-Pacific.

Drawn to the dark side: A molecular phylogeny of freshwater shrimps (Crustacea: Decapoda: Caridea: Atyidae) reveals frequent cave invasions and challenges current taxonomic hypotheses

Atyid freshwater shrimps are globally distributed and form an important part of freshwater ecosystems, particularly in the tropics and subtropics. Despite their widespread distribution and ecological importance, their phylogenetic relationships are largely unresolved. Here we present the first comprehensive molecular phylogeny of the Atyidae investigating the evolutionary relationships among 32 of the 42 genera using mitochondrial and nuclear markers. Our data indicate that the established classification of the Atyidae is in need of substantial taxonomic revision at all taxonomic levels. We suggest a new suprageneric systematization of atyids and discuss problematic issues at the generic level, particularly in the most speciose genus, Caridina. Molecular clock based divergence time estimates for atyids vary widely, but invariably support the assumption that atyids are an ancient freshwater lineage with an origin in the mid-Cretaceous at the very latest. Atyid distribution patterns are the result of instances of both long-distance dispersal and vicariance, depending largely on the reproductive mode of taxa. From an evolutionary perspective, the high frequency of independent origin of both a complete (landlocked) freshwater life cycle and a cave-dwelling mode of life is remarkable and unparalleled among crustaceans.

ADAPTIVE RADIATION AND ECOLOGICAL DIVERSIFICATION OF SULAWESI'S ANCIENT LAKE SHRIMPS

Ancient lakes are natural laboratories for the study of adaptive radiation. Recently, two lake systems on the Indonesian island Sulawesi have emerged as promising new model systems. A species flock of atyid freshwater shrimps in the Malili lake system comprises 15 colorful endemic taxa. Mitochondrial DNA data suggest two independent colonizations by riverine ancestors. Only one colonization event led to subsequent radiation into 14 species, while the second clade comprises just one species. The vast majority of species (n= 12) are habitat specialists, which are confined to the larger Malili clade and include all taxa with species‐specific color patterns and a restricted distribution within the five connected Malili lakes. Morphological, genetic, and ecological data are consistent with the existence of an adaptive radiation in the Malili lakes, involving the habitat‐specific diversification of trophic morphology. In addition to testing criteria for the recognition of an adaptive radiation, an ancestral state reconstruction reveals an equal probability for either a riverine generalist or a lacustrine specialist as ancestor of the large Malili clade, which is interpreted as indicative of an early stage of habitat specialization within this radiation. Finally, our results suggest that species diversification may have been primarily driven by ecological specialization and allopatric speciation.

Freshwater shrimp-sponge association from an ancient lake

Shrimp–sponge associations occur frequently in marine ecosystems, serving as model systems for the evolution of eusociality. Here, we describe the first known instance of such association in freshwater from an ancient lake in Indonesia. The shrimp Caridina spongicola forms an exclusive and probably commensal association with a yet undescribed spongillinid sponge. Phylogenetic and ecological data suggest a comparatively recent origin of both taxa. Climatic fluctuations may have facilitated speciation and occasional hybridization of the shrimp species, which is derived from a rock-dwelling ancestor. Their extremely localized occurrence in an increasingly disturbed area makes both taxa a conservation priority.

Phylogenetic and biogeographic relationships of subterranean and surface genera of Australian Atyidae (Crustacea : Decapoda : Caridea) inferred with mitochondrial DNA

The biogeographic and phylogenetic relationships of six of the eight Australian genera of freshwater shrimp from the family Atyidae were investigated using mitochondrial 16S rDNA and cytochrome oxidase I sequences. Previous studies on two of the epigean genera (Caridina, Paratya) indicate that Australian species have strong links to congenerics from outside, with Australian members of Paratya being monophyletic and Caridina polyphyletic. The present study found that the endemic Australian epigean genus Australatya forms a strong clade with Pacific ‘Atya-like’ genera (Atyoida, Atyopsis), and that the endemic Australian epigean genus Caridinides falls within a clade containing Caridina species from the Australian ‘indistincta’ group. The two hypogean genera included in this study (Parisia, Pycnisia) form a strong clade in all analyses, implying an Australian subterranean speciation. The possibility of a relationship between Parisia/Pycnisia and an Australian Caridina species may have implications for the monophyly of the highly disjunct genus Parisia (Australia, Madagascar, Philippines). Parisia may descend from local Caridina species and represent convergent morphologies.

The Species Flocks of the Viviparous Freshwater Gastropod Tylomelania (Mollusca: Cerithioidea: Pachychilidae) in the Ancient Lakes of Sulawesi, Indonesia: The Role of Geography, Trophic Morphology and Color as Driving Forces in Adaptive Radiation

The study of species flocks in island settings such as ancient lakes can contribute significantly to our understanding of fundamental evolutionary processes, such as speciation, radiation, adaptation, and coevolution. We here use endemic freshwater gastropods in ancient lakes on the Indonesian island of Sulawesi as models to gain insights into patterns and mechanisms of lacustrine diversification. In two central lake systems on the island, i.e., Lake Poso and the five connected Malili lakes, the pachychilid freshwater snail genus Tylomelania has radiated into a diverse endemic assemblage of c. 53 species of morphologically distinct viviparous gastropods. Molecular phylogenetic data revealed that independent and multiple colonizations of the two lake systems by fluviatile ancestors have led to four morphologically and ecologically diverse adaptive radiations, one in Lake Poso and three in the Malili system. The evolution of habitat preferences and trophic specialization most likely drive diversification in both systems, while geography, i.e., allopatric speciation, is a major factor in the spatially strongly structured Malili system. Highly characteristic lacustrine shell forms have evolved in all lakes through escalation, i.e., coevolution with molluscivorous crabs. The role of the conspicuous body coloration present mainly in Lake Poso species remains to be elucidated, specifically its potential role in diversification processes. Finally, the setting of the Sulawesi snail species flocks with two independent radiations under almost identical extrinsic conditions offers insights into parallel patterns of adaptive evolution. However, a major conservation effort will be required to preserve the lakes’ spectacular species for future research.

News from a small island – first record of a freshwater shrimp (Decapoda, Atyidae, Caridina) from Peleng, Banggai Islands, Indonesia

The Indonesian island Sulawesi is well known for its fascinating fauna. Among the atyid and palaemonid freshwater shrimps described from Sulawesi are also a number of endemic species. In contrast, freshwater shrimps have never been reported from the nearby and smaller Peleng Island. Here we describe Caridina thomasi sp. nov. as a first record of an atyid freshwater shrimp from Peleng and compare it with atyids from Sulawesi and other localities. The new species is probably endemic to the island and shows some characters never described in the genus Caridina before. However, a molecular phylogeny of atyid shrimps from the Indo‐West Pacific based on mitochondrial DNA (16S) places C. thomasi within a clade of typical species of Caridina. We tentatively assign the new species to the genus Caridina and discuss the possibility of future changes in the classification of species in this genus.

Epibiontic communities on the freshwater shrimp Caridina ensifera (Crustacea, Decapoda, Atyidae) from Lake Poso (Sulawesi, Indonesia)

The epibiont communities of the freshwater shrimp Caridina ensifera, endemic to Lake Poso (Sulawesi, Indonesia), were analysed for the first time based on their morphological and biometrical characteristics and taxonomic position. Seven ciliated protozoans and a rotifer were examined: three suctorian ciliate protozoan species (Acineta sulawesiensis, Podophrya maupasi, and Spelaeophrya polypoides), three peritrichs (Zoothamnium intermedium, Vorticella globosa, and Cothurnia compressa), a haptorid (Amphileptus fusidens), and the rotifer species Embata laticeps. A mean number of 314.6 epibionts was found per shrimp specimen. The distribution of the epibiont species on the surface of the basibiont was recorded, to allow calculation of the density on the different colonized individuals of C. ensifera and on each anatomical unit of the shrimp. The most abundant species, Zoothamnium intermedium and Acineta sulawesiensis, were also the ones most widely distributed. The statistical analysis showed that Zoothamnium, Acineta, Podophrya, and Embata were the epibiont genera most widely distributed on the basibiont, and the pairs of epibiont genera Zoothamnium–Embata, Podophrya–Acineta, Spelaeophrya–Amphileptus, and Cothurnia–Vorticella followed a similar pattern of distribution. There was a significant difference between the distribution patterns of the different epibiont species on the shrimp. The analysis of the densities of the epibionts throughout the longitudinal axis of the shrimp showed a gradient from the anterior to the posterior end of the body, and a significantly different distribution of each epibiont species. Their colonization follows a certain pattern of behaviour, the species occupying the available substratum, with particular requirements of each functional group, but with a trend resulting in equilibrium among species and groups, compensating for diversity and density. The possible adaptations of the epibionts, as well as the colonization patterns are discussed.