Surface to subsurface freshwater connections: phylogeographic and habitat analyses of Cambarus tenebrosus, a facultative cave-dwelling crayfish

This study examined the phylogeography and population demographics of Cambarus tenebrosus , which has an unusually large distribution for a freshwater crayfish species, encompassing the Interior Lowlands and Cumberland Plateau of the eastern United States. This facultative cave-dweller provides a unique perspective on the biologic connections between surface and subsurface freshwater ecosystems, which are considered to be highly imperiled due to pollution and habitat degradation. The 16S mitochondrial gene was sequenced for 233 individuals from 84 cave and 20 surface locations throughout the range, with most sampling concentrated around the Cumberland Plateau of the southern Appalachians, to assess conservation status of this species and examine the extent of gene flow between the two habitat types. Cave and surface populations formed a single monophyletic group relative to Cambarus striatus , and clades showed strong geographical associations, but lacked habitat structuring. Occupation of subterranean environments does not appear to be a recent event in the evolutionary history of the species. The large amount of genetic diversity within the species, coupled with its ability to inhabit surface and subsurface environments, suggests that this species may pose a threat as a possible invasive species in other karst-dominated landscapes.     

Avoidance of extinction through nonexistence: the use of museum specimens and molecular genetics to determine the taxonomic status of an endangered freshwater crayfish

We investigated the endangered status and taxonomic status of the freshwater crayfish Procambarus ferrugineus, a crayfish species considered for the candidate list of the Endangered Species Act. This species has a narrow distribution from central Arkansas, USA and is codistributed with its presumed sister species, Procambarus liberorum. We sampled extensively throughout the ranges of both primary burrowing species and collected mitochondrial DNA from a hypervariable fragment of the 16S gene from 109 individuals across 22 sites. We also collected data from a variable region of the 12S gene from a subset of the resulting 16S haplotypes. Due to our inability to sample what we considered P. ferrugineus in the field, we included museum specimens from the United States Natural History Museum of both P. ferrugineus and P. liberorum. Analyses of the resulting data suggested that these two species are indeed the same and we therefore synonymize them under the name of priority—P. liberorum. Additionally, our sampling discovered three new cryptic species from southwestern Arkansas all from the genus Procambarus. Nested clade phylogeographic analysis coupled with population genetic analyses suggested that P. liberorum has had three rounds of range expansion throughout the inferred evolutionary history. Using IUCN Red List criteria for conservation assessment, we conclude that the species P. liberorum should be considered stable, but with special concern because of habitat fragmentation and urbanization, small restricted range, and a moderate level of genetic diversity. Procambarus reimeri should be considered endangered due to its limited geographic range and the potential for a decline in suitable habitat. The three potentially newly discovered species should be considered data deficient until more information is obtained on their distributional limits and habitat requirements. Our study highlights the importance of thorough geographic and taxonomic sampling coupled with the utility of collecting data from museum specimens to reach robust taxonomic and conservation conclusions for endangered species.     

Phylogeography of Sardinian cave salamanders (genus Hydromantes) is mainly determined by geomorphology

Detecting the factors that determine the interruption of gene flow between populations is key to understanding how speciation occurs. In this context, caves are an excellent system for studying processes of colonization, differentiation and speciation, since they represent discrete geographical units often with known geological histories. Here, we asked whether discontinuous calcareous areas and cave systems represent major barriers to gene flow within and among the five species of Sardinian cave salamanders (genus Hydromantes) and whether intraspecific genetic structure parallels geographic distance within and among caves. We generated mitochondrial cytochrome b gene sequences from 184 individuals representing 48 populations, and used a Bayesian phylogeographic approach to infer possible areas of cladogenesis for these species and reconstruct historical and current dispersal routes among distinct populations. Our results show deep genetic divergence within and among all Sardinian cave salamander species, which can mostly be attributed to the effects of mountains and discontinuities in major calcareous areas and cave systems acting as barriers to gene flow. While these salamander species can also occur outside caves, our results indicate that there is a very poor dispersal of these species between separate cave systems.     

Evidence for speciation underground in diving beetles (Dytiscidae) from a subterranean archipelago

Most subterranean animals are assumed to have evolved from surface ancestors following colonization of a cave system; however, very few studies have raised the possibility of “subterranean speciation” in underground habitats (i.e., obligate cave‐dwelling organisms [troglobionts] descended from troglobiotic ancestors). Numerous endemic subterranean diving beetle species from spatially discrete calcrete aquifers in Western Australia (stygobionts) have evolved independently from surface ancestors; however, several cases of sympatric sister species raise the possibility of subterranean speciation. We tested this hypothesis using vision (phototransduction) genes that are evolving under neutral processes in subterranean species and purifying selection in surface species. Using sequence data from 32 subterranean and five surface species in the genus Paroster (Dytiscidae), we identified deleterious mutations in long wavelength opsin (lwop), arrestin 1 (arr1), and arrestin 2 (arr2) shared by a sympatric sister‐species triplet, arr1 shared by a sympatric sister‐species pair, and lwop and arr2 shared among closely related species in adjacent calcrete aquifers. In all cases, a common ancestor possessed the function‐altering mutations, implying they were already adapted to aphotic environments. Our study represents one of the first confirmed cases of subterranean speciation in cave insects. The assessment of genes undergoing pseudogenization provides a novel way of testing modes of speciation and the history of diversification in blind cave animals.     

Biogeography of subterranean decapods in North and Central America and the Caribbean region (Caridea,Astacidea, Brachyura)

A significant number of decapod crustaceans (81 troglobites and 58 other cavernicoles) has been described from various subterranean waters in North and Central America (United States south to Costa Rica) and from the islands in the western north Atlantic and the Caribbean Sea, posing puzzling questions concerning their evolution and biogeography. Of these troglobitic species, 36 are shrimps (1 procarid, 11 atyids, 2 agostocarids, 15 palaemonids, 2 alpheids, 5 hippolytids), 35 are cambarid crayfishes, and 10 are crabs (1 grapsid, 7 pseudothelphusids, 2 trichodactylids). They are known to occur in caves, springs, cenotes, blue holes, anchialine environments, and various crevicular habitats in localized areas throughout the region. Many, if not the majority, of the troglobites appear to have arisen independently from epigean progenitors rather than sharing common subterranean precursors.     

Reduction in the metabolic levels due to phenotypic plasticity in the Pyrenean newt,Calotriton asper,during cave colonization

According to theories on cave adaptation, cave organisms are expected to develop a lower metabolic rate compared to surface organisms as an adaptation to food scarcity in the subterranean environments. To test this hypothesis, we compared the oxygen consumption rates of the surface and subterranean populations of a surface‐dwelling species, the newt Calotriton asper, occasionally found in caves. In this study, we designed a new experimental setup in which animals with free movement were monitored for several days in a respirometer. First, we measured the metabolic rates of individuals from the surface and subterranean populations, both maintained for eight years in captivity in a natural cave. We then tested individuals from these populations immediately after they were caught and one year later while being maintained in the cave. We found that the surface individuals that acclimated to the cave significantly reduced their oxygen consumption, whereas individuals from the subterranean population maintained in the cave under a light/dark cycle did not significantly modify their metabolic rates. Second, we compared these metabolic rates to those of an obligate subterranean salamander (Proteus anguinus), a surface aquatic Urodel (Ambystoma mexicanum), and a fish species (Gobio occitaniae) as references for surface organisms from different phyla. As predicted, we found differences between the subterranean and surface species, and the metabolic rates of surface and subterranean C. asper populations were between those of the obligate subterranean and surface species. These results suggest that the plasticity of the metabolism observed in surface C. asper was neither directly due to food availability in our experiments nor the light/dark conditions, but due to static temperatures. Moreover, we suggest that this adjustment of the metabolic level at a temperature close to the thermal optimum may further allow individual species to cope with the food limitations of the subterranean environment.     

Shrimps down under: evolutionary relationships of subterranean crustaceans from Western Australia (Decapoda: Atyidae: Stygiocaris)

Background

We investigated the large and small scale evolutionary relationships of the endemic Western Australian subterranean shrimp genus Stygiocaris (Atyidae) using nuclear and mitochondrial genes. Stygiocaris is part of the unique cave biota of the coastal, anchialine, limestones of the Cape Range and Barrow Island, most of whose nearest evolutionary relations are found in coastal caves of the distant North Atlantic. The dominance of atyids in tropical waters and their food resources suggest they are pivotal in understanding these groundwater ecosystems.

Methodology/Principle Findings

Our nuclear and mitochondrial analyses all recovered the Mexican cave genus Typhlatya as the sister taxon of Stygiocaris, rather than any of the numerous surface and cave atyids from Australia or the Indo-Pacific region. The two described Stygiocaris species were recovered as monophyletic, and a third, cryptic, species was discovered at a single site, which has very different physiochemical properties from the sites hosting the two described species.

Conclusions/Significance

Our findings suggest that Stygiocaris and Typhlatya may descend from a common ancestor that lived in the coastal marine habitat of the ancient Tethys Sea, and were subsequently separated by plate tectonic movements. This vicariant process is commonly thought to explain the many disjunct anchialine faunas, but has rarely been demonstrated using phylogenetic techniques. The Cape Range''s geological dynamism, which is probably responsible for the speciation of the various Stygiocaris species, has also led to geographic population structure within species. In particular, Stygiocaris lancifera is split into northern and southern groups, which correspond to population splits within other sympatric subterranean taxa.     

A narrow hybrid zone between two crayfish species from a Mexican cave

In Northern Chiapas (Mexico), two newly discovered species of Procambarus crayfish inhabit a subterranean stream. These species can be morphologically distinguished only by comparing extreme phenotypes (dark, thick-eyed, surface dwelling-like individuals vs light, elongated, microphtalmic, cave dwelling-like individuals). Individuals with intermediate phenotypes co-occur with those exhibiting extreme phenotypes. Crayfish were assayed electrophoretically and individual patterns at 23 gene loci were obtained. Unusually high levels of heterozygosity in both species and a clear discrimination between the two gene pools were revealed. The relationships between individuals were investigated by means of multivariate analysis on individual multilocus genotype profiles. Results showed the occurrence of individuals genetically intermediate between the two major clusters, which shared allozymic variants with both species. Due to the occurrence of alternative alleles in the two gene pools, we could quantify patterns of introgression, which revealed asymmetric gene flow between the two species. Moreover, differential levels of introgression in subsamples within the surface-like species were found: most introgressed individuals came from the inner section of the cave, where the two species were greatly mixed. These results are also discussed in reference to the morphometric results from a companion paper. A possible evolutionary pathway, leading to the situation in this cave, and possibly in neighbouring cave systems, is outlined. The hypothesis of a past history of allopatric divergence from a common ancestor and a subsequent secondary contact between these two Procambarus species is supported by geological studies. Crayfish sympatry and competitive exclusion are also discussed.     

Population genetic structure of the endangered crayfish Austropotamobius pallipes in France based on microsatellite variation: biogeographical inferences and conservation implications

1. One important goal in conservation biology is to characterise evolutionary lineages within endangered species before management decisions are taken. Here, we assess population differentiation in the freshwater crayfish Austropotamobius pallipes, an endangered species endemic to western Europe and provide valuable information for the conservation of French populations. 2. Analysis of five microsatellite loci in 44 populations revealed very different within population levels of genetic diversity (0.000 < H₀ < 0.564). Two groups, corresponding to northern and southern French populations, showed a high degree of genetic differentiation in both allele frequencies and allele sizes. Comparison of these results with previous studies of A. pallipes strongly suggests that the divergence between northern and southern populations could have occurred during the last glaciation period of the Pleistocene from one Atlantic and one Mediterranean refuge. 3. Evidence for genetic admixture between these two lineages was revealed by correspondence analyses in southern populations, probably as the result of artificial translocations. 4. French populations appeared significantly differentiated among the different river drainages and were highly structured within rivers. The impact of population size, population bottlenecks and founder events on the population genetic differentiation are discussed. 5. Based on these results, we propose the designation of two evolutionarily significant units for A. pallipes in France. Our data also support the maintenance of separate demographic management strategies for crayfish inhabiting different river systems. However, genetic analyses will have to be combined with demographic and ecological data for sustainable conservation programmes.     

Heat tolerance and acclimation capacity in subterranean arthropods living under common and stable thermal conditions

Cave‐dwelling ectotherms, which have evolved for millions of years under stable thermal conditions, could be expected to have adjusted their physiological limits to the narrow range of temperatures they experience and to be highly vulnerable to global warming. However, most of the few existing studies on thermal tolerance in subterranean invertebrates highlight that despite the fact that they show lower heat tolerance than most surface‐dwelling species, their upper thermal limits are generally not adjusted to ambient temperature. The question remains to what extent this pattern is common across subterranean invertebrates. We studied basal heat tolerance and its plasticity in four species of distant arthropod groups (Coleoptera, Diplopoda, and Collembola) with different evolutionary histories but under similar selection pressures, as they have been exposed to the same constant environmental conditions for a long time. Adults were exposed at different temperatures for 1 week to determine upper lethal temperatures. Then, individuals from previous sublethal treatments were transferred to a higher temperature to determine acclimation capacity. Upper lethal temperatures of three of the studied species were similar to those reported for other subterranean species (between 20 and 25°C) and widely exceeded the cave temperature (13–14°C). The diplopod species showed the highest long‐term heat tolerance detected so far for a troglobiont (i.e., obligate subterranean) species (median lethal temperature after 7 days exposure: 28°C) and a positive acclimation response. Our results agree with previous studies showing that heat tolerance in subterranean species is not determined by environmental conditions. Thus, subterranean species, even those living under similar climatic conditions, might be differently affected by global warming.     

An invaded invader: high prevalence of entocytherid ostracods on the red swamp crayfish <Emphasis Type="Italic">Procambarus clarkii</Emphasis> (Girard, 1852) in the Eastern Iberian Peninsula

The American red swamp crayfish Procambarus clarkii (Girard, 1852) was introduced in 1973 into the Iberian Peninsula for commercial purposes. As a result of both the expansion from the Iberian Peninsula and, probably, further introductions in other European countries, now it is widely distributed throughout much of Europe. The ecological impacts of this invading crayfish have received increasing attention, but nothing is known about its symbiotic entocytherid ostracods outside the American continent. The present survey has examined more than 200 crayfishes from 12 localities distributed over a wide area of Eastern Spain. Entocytherid ostracods were extracted from individual crayfishes and they were identified, counted, assigned to developmental instars and sexed. In all the study locations but one, we found at least one crayfish individual infected by entocytherid ostracods and the species determined was the same in all cases: Ankylocythere sinuosa (Rioja, 1942). The number of ostracods on individual P. clarkii varied notably in relation to crayfish size and also differed significantly among sampling sites. The crayfish size effects on ostracod densities might be related to the amount of resources and to the crayfish age and moulting frequency affecting ostracod distribution and population structure. In addition, the spatial variation in ostracod densities could also be related to site-specific habitat traits and the variability of crayfish population dynamics. Our study represents the first citation of an alien entocytherid species in Europe and demonstrates its wide distribution in the Iberian Peninsula. Further research is needed to know the potential effects of this ostracod species on the ecology of P. clarkii and of native species, with implications on the management of this aquatic invader.     

Home-field advantage: native signal crayfish (Pacifastacus leniusculus) out consume newly introduced crayfishes for invasive Chinese mystery snail (Bellamya chinensis)

The introduction of non-indigenous plants, animals and pathogens is one of today’s most pressing environmental challenges. Freshwater ecologists are challenged to predict the potential consequences of species invasions because many ecosystems increasingly support novel assemblages of native and non-native species that are likely to interact in complex ways. In this study we evaluated how native signal crayfish (Pacifastacus leniusculus) and non-native red swamp crayfish (Procambarus clarkii) and northern crayfish (Orconectes virilis) utilize a novel prey resource: the non-native Chinese mystery snail (Bellamya chinensis). All species are widespread in the United States, as well as globally, and recent surveys have discovered them co-occurring in lakes of Washington State. A series of mesocosm experiments revealed that crayfish are able to consume B. chinensis, despite the snail’s large size, thick outer shell and trapdoor defense behaviour. Crayfish exhibited size-selective predation whereby consumption levels decreased with increasing snail size; a common pattern among decapod predators. Comparison of prey profitability curves—defined as the yield of food (weight of snail tissue) per second of feeding time (the time taken to crack the shell and consume the contents)—suggests that small and very large snails may represent the most profitable prey choice. By contrast, previous studies have reported the opposite pattern for crayfish consumption on thin-shelled snails. For all snail size classes, we found that native P. leniusculus and invasive O. virilis consumed greater numbers of snails than invasive P. clarkii. Moreover, P. leniusculus consistently handled and consumed snails at a faster pace compared to both invasive crayfishes across the range of snail sizes examined in our study. These results suggest not only that B. chinensis is a suitable food source for crayfish, but also that native P. leniusculus may ultimately out-consume invasive crayfishes for this new prey resource.     

Evolution in caves: Darwin’s ‘wrecks of ancient life’ in the molecular era

Cave animals have historically attracted the attention of evolutionary biologists because of their bizarre ‘regressive’ characters and convergent evolution. However, understanding of their biogeographic and evolutionary history, including mechanisms of speciation, has remained elusive. In the last decade, molecular data have been obtained for subterranean taxa and their surface relatives, which have allowed some of the classical debates on the evolution of cave fauna to be revisited. Here, we review some of the major studies, focusing on the contribution of phylogeography in the following areas: biogeographic history and the relative roles of dispersal and vicariance, colonization history, cryptic species diversity and modes of speciation of cave animals. We further consider the limitations of current research and prospects for the future. Phylogeographic studies have confirmed that cave species are often cryptic, with highly restricted distributions, but have also shown that their divergence and potential speciation may occur despite the presence of gene flow from surface populations. Significantly, phylogeographic studies have provided evidence for speciation and adaptive evolution within the confines of cave environments, questioning the assumption that cave species evolved directly from surface ancestors. Recent technical developments involving ‘next generation’ DNA sequencing and theoretical developments in coalescent and population modelling are likely to revolutionize the field further, particularly in the study of speciation and the genetic basis of adaptation and convergent evolution within subterranean habitats. In summary, phylogeographic studies have provided an unprecedented insight into the evolution of these unique fauna, and the future of the field should be inspiring and data rich.     

Population genomic analysis suggests strong influence of river network on spatial distribution of genetic variation in invasive saltcedar across the southwestern United States

Understanding the complex influences of landscape and anthropogenic elements that shape the population genetic structure of invasive species provides insight into patterns of colonization and spread. The application of landscape genomics techniques to these questions may offer detailed, previously undocumented insights into factors influencing species invasions. We investigated the spatial pattern of genetic variation and the influences of landscape factors on population similarity in an invasive riparian shrub, saltcedar (Tamarix L.) by analysing 1,997 genomewide SNP markers for 259 individuals from 25 populations collected throughout the southwestern United States. Our results revealed a broad‐scale spatial genetic differentiation of saltcedar populations between the Colorado and Rio Grande river basins and identified potential barriers to population similarity along both river systems. River pathways most strongly contributed to population similarity. In contrast, low temperature and dams likely served as barriers to population similarity. We hypothesize that large‐scale geographic patterns in genetic diversity resulted from a combination of early introductions from distinct populations, the subsequent influence of natural selection, dispersal barriers and founder effects during range expansion.     

Phylogeography of subterranean and surface populations of water lice Asellus aquaticus (Crustacea: Isopoda)

The water louse Asellus aquaticus is a widespread, euryoecious species, mostly uniform throughout its range. However, six subspecies are known from the Dinaric karst in the northwestern Balkans. They include some specialized subterranean populations. The pattern of genetic variation among subterranean and surface populations in this hydrographically highly fragmented karst region was investigated using a 653 bp fragment of the mitochondrial gene (COI). Sequencing of 168 individuals from 25 localities revealed 72 haplotypes. amova and methods of phylogenetic reconstruction all uncovered hydrographic structuring of genetic variation of the populations. Nested clade analysis pointed out several fragmentation events, along with some range expansions within hydrographical systems. By superimposing the subterranean mode of life on the phylogeographical pattern, three independent cave colonizations could be inferred within a distance of < 100 km. Caves were invaded after the ancestral surface populations became isolated through vicariant fragmentation. A possible scenario of hydrographic history of the region was constructed combining the molecular data with palaeogeographical information.     

Intensive trapping and increased fish predation cause massive population decline of an invasive crayfish

1. Invasive species frequently have adverse impacts on native communities and ecosystems. Management options are often limited. Our goal is to evaluate the effect of intensive trapping and fish predation on the population dynamics of an invasive crayfish. 2. From 2001 to 2005, we removed invasive rusty crayfish (Orconectes rusticus) by trapping in Sparkling Lake in northern WI. In addition, the Wisconsin Department of Natural Resources restricted harvest of fish species known to consume crayfish, thereby increasing predation on crayfish that are too small to trap. 3. After an initial increase, catch rates of rusty crayfish declined by approximately 95%, from 11 crayfish per trap per day in 2002 to 0.65 in 2004. The catch rate in 2005 remained low at 0.5 crayfish per trap. Females comprised nearly 50% of the catch from 2002 to 2004. Unlike rusty crayfish in Sparkling Lake, catch rates of O. rusticus and Orconectes propinquus in three nearby lakes increased or remained relatively constant over the 5‐year removal period. 4. We also examined the influence of habitat and temperature on crayfish catch rates. Catch rates were highest at water temperatures between 20 and 25 °C and on cobble, log or macrophyte habitats that may serve as refuge from fish predation. 5. Five summers of intensive trapping and fisheries management practices reduced abundances, but did not extirpate rusty crayfish in Sparkling Lake. To determine the potential of trapping as a management option for invasive crayfishes, these methods must be tested in other systems.     

Phylogenetic evidence from freshwater crayfishes that cave adaptation is not an evolutionary dead‐end

Caves are perceived as isolated, extreme habitats with a uniquely specialized biota, which long ago led to the idea that caves are “evolutionary dead‐ends.” This implies that cave‐adapted taxa may be doomed for extinction before they can diversify or transition to a more stable state. However, this hypothesis has not been explicitly tested in a phylogenetic framework with multiple independently evolved cave‐dwelling groups. Here, we use the freshwater crayfish, a group with dozens of cave‐dwelling species in multiple lineages, as a system to test this hypothesis. We consider historical patterns of lineage diversification and habitat transition as well as current patterns of geographic range size. We find that while cave‐dwelling lineages have small relative range sizes and rarely transition back to the surface, they exhibit remarkably similar diversification patterns to those of other habitat types and appear to be able to maintain a diversity of lineages through time. This suggests that cave adaptation is not a “dead‐end” for freshwater crayfish, which has positive implications for our understanding of biodiversity and conservation in cave habitats.     

Recent divergence with gene flow in Tennessee cave salamanders (Plethodontidae: Gyrinophilus) inferred from gene genealogies

Cave organisms occupy a special place in evolutionary biology because convergent morphologies of many species demonstrate repeatability in evolution even as they obscure phylogenetic relationships. The origin of specialized cave-dwelling species also raises the issue of the relative importance of isolation vs. natural selection in speciation. Two alternative hypotheses describe the origin of subterranean species. The 'climate-relict' model proposes allopatric speciation after populations of cold-adapted species become stranded in caves due to climate change. The 'adaptive-shift' model proposes parapatric speciation driven by divergent selection between subterranean and surface habitats. Our study of the Tennessee cave salamander complex shows that the three nominal forms (Gyrinophilus palleucus palleucus, G. p. necturoides, and G. gulolineatus) arose recently and are genealogically nested within the epigean (surface-dwelling) species, G. porphyriticus. Short branch lengths and discordant gene trees were consistent with a complex history involving gene flow between diverging forms. Results of coalescent-based analysis of the distribution of haplotypes among groups reject the allopatric speciation model and support continuous or recurrent genetic exchange during divergence. These results strongly favour the hypothesis that Tennessee cave salamanders originated from spring salamanders via divergence with gene flow.     

Genetic analysis of the threatened American hart's-tongue fern (Asplenium scolopendrium var. americanum [Fernald] Kartesz and Gandhi): Insights into its mating system and implications for conservation

American hart's-tongue fern (AHTF) is one of the rarest ferns in the United States and concern over its conservation and management has highlighted the need for genetic analysis. Genetic analysis also provides insights into the species' mating system which contributes to our understanding of its rarity and persistence. We analyzed 88 individuals from 11 populations in NY and MI based on variations in 108 loci as revealed through ISSR markers using Nei's gene diversity index, percent polymorphic loci and other measures. Low genetic diversity predominates in the populations from NY, and even lower for the populations in MI. Our results also indicate that AHTF from NY and MI are genetically differentiated from each other, as well as the populations within them. There is no positive correlation between genetic and geographic distances, as well as between genetic distance and census population size. The significantly high among population genetic variation and low gene flow value are common indicators of a predominant inbreeding mating strategy within populations, limited spore dispersal, and genetic drift. Our results also indicate that each AHTF population is an important contributor to the overall genetic variation of the species and thus, represents a significant unit for conservation efforts.     

Re‐examining extreme longevity of the cave crayfish Orconectes australis using new mark–recapture data: a lesson on the limitations of iterative size‐at‐age models

1. Centenarian species, defined as those taxa with life spans that frequently exceed 100 years, have long been of interest to ecologists because they represent an extreme end point in a continuum of life history strategies. One frequently reported example of a freshwater centenarian is the obligate cave crayfish Orconectes australis, with a maximum longevity reported to exceed 176 years. As a consequence of its reported longevity, O. australis has been used as a textbook example of life history adaptation to the organic‐carbon limitation that characterises many cave‐stream food webs. 2. Despite being widely reported, uncertainties surround the original estimates of longevity for O. australis, which were based on a single study dating from the mid‐1970s. In the present study, we re‐evaluated the growth rate, time‐to‐maturity, female age‐at‐first‐reproduction and longevity of O. australis using a mark–recapture study of more than 5 years based upon more than 3800 free‐ranging individuals from three isolated cave streams in the south‐eastern United States. 3. The results of our study indicate that accurate estimates of the longevity of O. australis are ≤22 years, with only a small proportion of individuals (<5%) exceeding this age. Our estimates for female time‐to‐maturity (4–5 years) and age‐at‐first‐reproduction (5–6 years) are also substantially lower than earlier estimates. 4. These new data indicate that the age thresholds for life history events of O. australis are comparable to other estimates for a modest assemblage of cave and surface species of crayfish for which credible age estimate exists, suggesting that a cave environment per se is not required for the evolution of extreme longevity in crayfish.