Cave Populations Research Articles

Convergence on reduced stress behavior in the Mexican blind cavefish

Responding appropriately to stress is essential for survival, yet in pathological states, these responses can develop into debilitating conditions such as post-traumatic stress disorder and generalized anxiety. While genetic models have provided insight into the neurochemical and neuroanatomical pathways that underlie stress, little is known about how evolutionary processes and naturally occurring variation contribute to the diverse responses to stressful stimuli observed in the animal kingdom. The Mexican cavefish is a powerful system to address how altered genetic and neuronal systems can give rise to altered behaviors. When introduced into a novel tank, surface fish and cavefish display a stereotypic stress response, characterized by reduced exploratory behavior and increased immobility, akin to "freezing". The stress response in cave and surface forms is reduced by pharmacological treatment with the anxiolytic drug, buspirone, fortifying the notion that behavior in the assay represents a conserved stress state. We find that cave populations display reduced behavioral measures of stress compared to surface conspecifics, including increased time in the top half of the tank and fewer periods of immobility. Further, reduced stress responses are observed in multiple independently derived cavefish populations, suggesting convergence on loss of behavioral stress responses in the novel tank assay. These findings provide evidence of a naturally occurring species with two drastically different forms in which a shift in predator-rich ecology to one with few predators corresponds to a reduction in stress behavior.

Diversity of Potamolithus (Littorinimorpha, Truncatelloidea) in a high-diversity spot for troglobites in southeastern Brazil: role of habitat fragmentation in the origin of subterranean fauna, and conservation status

The Alto Ribeira karst area, southeastern Brazil, is a high-diversity area for troglobites. Three species of freshwater gastropodsPotamolithusoccur in the area:P.ribeirensis, only found in epigean waters at the Iporanga and Ribeira rivers;P.troglobius, which is endemic to the Areias cave system; andP.karsticus, a troglophilic species from Calcário Branco Cave and an epigean stream nearby. We investigated their distribution based on shell morphology and internal anatomy of epigean species, troglophilic populations, and troglobitic species. Distribution patterns ofPotamolithuswere compared to those of other aquatic taxa from the region (such as crustaceans and fishes). Besides the three species already described for the region, we recorded 12 additional ones, for a total of 15 species/morphs (six troglobites, seven troglophiles, and two epigean).Potamolithusspp. are restricted to micro-basins and/or caves, showing small areas of distribution and probably a high degree of endemism. Geomorphology (irregular landscape, with limestone outcrops intercalated with insoluble rocks, which probably act as geographic barriers for cave populations), paleoclimatic evidence, and ecological/biological factors, such as the low degree of mobility of these gastropods (sedentary habit), explain the distributional patterns. We observed troglomorphisms such as reduction/absence of eyes and pigmentation (body and periostracum), and a coiled intestine. Apparently, there is no cause-and-effect between miniaturization and intestine coiling forPotamolithus, in contrast to observations for other cave snails.Potamolithussnails are threatened in the region due to water pollution, uncontrolled tourism, and overcollection.

Behavioural changes controlled by catecholaminergic systems explain recurrent loss of pigmentation in cavefish.

Multiple cave populations of the teleost Astyanax mexicanus have repeatedly reduced or lost eye and body pigmentation during adaptation to dark caves. Albinism, the complete absence of melanin pigmentation, is controlled by loss-of-function mutations in the oca2 gene. The mutation is accompanied by an increase in the melanin synthesis precursor l-tyrosine, which is also a precursor for catecholamine synthesis. In this study, we show a relationship between pigmentation loss, enhanced catecholamine synthesis and responsiveness to anaesthesia, determined as a proxy for catecholamine-related behaviours. We demonstrate that anaesthesia resistance (AR) is enhanced in multiple depigmented and albino cavefish (CF), inversely proportional to the degree of pigmentation loss, controlled by the oca2 gene, and can be modulated by experimental manipulations of l-tyrosine or the catecholamine norepinephrine (NE). Moreover, NE is increased in the brains of multiple albino and depigmented CF relative to surface fish. The results provide new insights into the evolution of pigment modification because NE controls a suite of adaptive behaviours similar to AR that may represent a target of natural selection. Thus, understanding the relationship between loss of pigmentation and AR may provide insight into the role of natural selection in the evolution of albinism via a melanin-catecholamine trade-off.

Evidence for late Pleistocene origin of Astyanax mexicanus cavefish

BackgroundCavefish populations belonging to the Mexican tetra species Astyanax mexicanus are outstanding models to study the tempo and mode of adaptation to a radical environmental change. They are currently assigned to two main groups, the so-called “old” and “new” lineages, which would have populated several caves independently and at different times. However, we do not have yet accurate estimations of the time frames of evolution of these populations.ResultsWe reanalyzed the geographic distribution of mitochondrial and nuclear DNA polymorphisms and we found that these data do not support the existence of two cavefish lineages. Using IMa2, a program that allows dating population divergence in addition to demographic parameters, we found that microsatellite polymorphism strongly supports a very recent origin of cave populations (< 20,000 years). We identified a large number of single-nucleotide polymorphisms (SNPs) in transcript sequences of pools of embryos (Pool-seq) belonging to Pachón cave population and a surface population from Texas. Based on summary statistics that can be computed with this SNP data set together with simulations of evolution of SNP polymorphisms in two recently isolated populations, we looked for sets of demographic parameters that allow the computation of summary statistics with simulated populations that are similar to the ones with the sampled populations. In most simulations for which we could find a good fit between the summary statistics of observed and simulated data, the best fit occurred when the divergence between simulated populations was less than 30,000 years.ConclusionsAlthough it is often assumed that some cave populations have a very ancient origin, a recent origin of these populations is strongly supported by our analyses of independent sets of nuclear DNA polymorphism. Moreover, the observation of two divergent haplogroups of mitochondrial and nuclear genes with different geographic distributions support a recent admixture of two divergent surface populations, before the isolation of cave populations. If cave populations are indeed only several thousand years old, many phenotypic changes observed in cavefish would thus have mainly involved the fixation of genetic variants present in surface fish populations and within a very short period of time.

Fluctuating asymmetry as a bio-marker to account for in conservation and management of cave-dwelling species

The applicability of fluctuating asymmetry (FA) in conservation biology as a bio-marker and an early warning system have been examined in various groups of animals. However, cave-dwelling invertebrates have gotten little attention and yet caves have no biological management. Thus, developing a bio-marker to identify early responses of cave-dwelling species to stress provides a valuable tool to account for in future conservation and management programs. We examined whether FA can be used as a bio-marker of relaxed selection for cave-dwelling invertebrates. Specifically, we compared FA levels of pedipalps and two segments of chelicerae (chelicel1 and chelicel2) between cave and surface habitats and among populations in a troglophilic harvestman specie, Paranemastoma sillii sillii (Herman, 1871). Under the assumption that cave environment exerts relaxed selection we hypothesised that cave-dwelling harvestmen express higher degree of FA than surface-dwelling harvestmen. Because female and male harvestmen use the pediplaps differently, we assumed sex-specific selective pressures and further examined the effect of sex and habitat (cave vs surface) and sex interaction on FA levels. We hypothesised no differences in the levels of FA among harvestman cave populations, because of the idea that relaxed selection is responsible for higher levels of FA in cave-dwelling harvestmen rather than environmental stress. We found significant habitat sex interactions in the FA of the pedipalp. Interactions of population and sex had a significant effect on pedipalp and chelicel2 FA. These results partially support the idea that FA responds to differences in the strength of selection. Although we cannot fully disentangle the mechanisms of natural selection affecting FA and the study of trait asymmetry should be combined with studies of other sources of stress (i.e. genetic stress, predation, prey availability) we conclude that FA could be a bioindicator to be used as a tool in conservation and management of cave.

Insulin resistance in cavefish as an adaptation to a nutrient-limited environment.

Periodic food shortages are a major challenge faced by organisms in natural habitats. Cave-dwelling animals must withstand long periods of nutrient deprivation, as-in the absence of photosynthesis-caves depend on external energy sources such as seasonal floods. Here we show that cave-adapted populations of the Mexican tetra, Astyanax mexicanus, have dysregulated blood glucose homeostasis and are insulin-resistant compared to river-adapted populations. We found that multiple cave populations carry a mutation in the insulin receptor that leads to decreased insulin binding in vitro and contributes to hyperglycaemia. Hybrid fish from surface-cave crosses carrying this mutation weigh more than non-carriers, and zebrafish genetically engineered to carry the mutation have increased body weight and insulin resistance. Higher body weight may be advantageous in caves as a strategy to cope with an infrequent food supply. In humans, the identical mutation in the insulin receptor leads to a severe form of insulin resistance and reduced lifespan. However, cavefish have a similar lifespan to surface fish and do not accumulate the advanced glycation end-products in the blood that are typically associated with the progression of diabetes-associated pathologies. Our findings suggest that diminished insulin signalling is beneficial in a nutrient-limited environment and that cavefish may have acquired compensatory mechanisms that enable them to circumvent the typical negative effects associated with failure to regulate blood glucose levels.

CRISPR mutagenesis confirms the role of oca2 in melanin pigmentation in Astyanax mexicanus

Understanding the genetic basis of trait evolution is critical to identifying the mechanisms that generated the immense amount of diversity observable in the living world. However, genetically manipulating organisms from natural populations with evolutionary adaptations remains a significant challenge. Astyanax mexicanus exists in two interfertile forms, a surface-dwelling form and multiple independently evolved cave-dwelling forms. Cavefish have evolved a number of morphological and behavioral traits and multiple quantitative trait loci (QTL) analyses have been performed to identify loci underlying these traits. These studies provide a unique opportunity to identify and test candidate genes for these cave-specific traits. We have leveraged the CRISPR/Cas9 genome editing techniques to characterize the effects of mutations in oculocutaneous albinism II (oca2), a candidate gene hypothesized to be responsible for the evolution of albinism in A. mexicanus cave populations. We generated oca2 mutant surface A. mexicanus. Surface fish with oca2 mutations are albino due to a disruption in the first step of the melanin synthesis pathway, the same step that is disrupted in albino cavefish. Hybrid offspring from crosses between oca2 mutant surface and cavefish are albino, definitively demonstrating the role of this gene in the evolution of albinism in this species. This research elucidates the role oca2 plays in pigmentation in fish, and establishes that this gene is solely responsible for the evolution of albinism in multiple cavefish populations. Finally, it demonstrates the utility of using genome editing to investigate the genetic basis of trait evolution.

Hypocretin underlies the evolution of sleep loss in the Mexican cavefish

The duration of sleep varies dramatically between species, yet little is known about the genetic basis or evolutionary factors driving this variation in behavior. The Mexican cavefish, Astyanax mexicanus, exists as surface populations that inhabit rivers, and multiple cave populations with convergent evolution on sleep loss. The number of Hypocretin/Orexin (HCRT)-positive hypothalamic neurons is increased significantly in cavefish, and HCRT is upregulated at both the transcript and protein levels. Pharmacological or genetic inhibition of HCRT signaling increases sleep in cavefish, suggesting enhanced HCRT signaling underlies the evolution of sleep loss. Ablation of the lateral line or starvation, manipulations that selectively promote sleep in cavefish, inhibit hcrt expression in cavefish while having little effect on surface fish. These findings provide the first evidence of genetic and neuronal changes that contribute to the evolution of sleep loss, and support a conserved role for HCRT in sleep regulation.

Species delimitation in the morphologically conserved Coecobrya (Collembola: Entomobryidae): A case study integrating morphology and molecular traits to advance current taxonomy

Traditional species delimitation only based on morphological diagnostics does not fully meet the needs of modern taxonomy. Cryptic diversity revealed by molecular evidence has been increasingly discovered in many groups; however, subsequent species description is often lacking because of inadequate taxonomy and being devoid of operational criteria. In this study, we focus on the collembolan Coecobrya which has been suspected to be a species complex living on cave guanos. Our study aimed to integrate both morphological and molecular character traits to explore this group across geographically separated cave populations. Among seven sampled populations, only minor chaetotaxic differences were detected, and between populations, there was partial overlap of discriminating characters. However, using three genes (COI, 16S and 28S), we consistently recovered across distance‐ and evolutionary model‐based molecular delimitations seven molecular lineages, corresponding to seven candidate morphospecies. A final seven‐species hypothesis was validated and seven new species were described: Coecobrya phanthuratensis sp. n., Coecobrya ranongica sp. n., Coecobrya donyoa sp. n., Coecobrya khaopaela sp. n., Coecobrya specusincola sp. n., Coecobrya khromwanaramica sp. n. and Coecobrya promdami sp. n. A tentative taxonomic workflow integrating multiple lines of evidence is proposed to facilitate the subsequent formal species description for Collembola. Unified species concept is preferable to accommodate most species concepts, delimitation criteria and data analysis methods. In practice, DNA‐based diagnoses are recommended as the standard component for the current taxonomy of Collembola, particularly within morphologically conserved groups.

The role of isolation on contrasting phylogeographic patterns in two cave crustaceans

BackgroundThe underlying mechanisms and processes that prompt the colonisation of extreme environments, such as caves, constitute major research themes of evolutionary biology and biospeleology. The special adaptations required to survive in subterranean environments (low food availability, hypoxic waters, permanent darkness), and the geographical isolation of caves, nominate cave biodiversity as ideal subjects to answer long-standing questions concerning the interplay amongst adaptation, biogeography, and evolution. The present project aims to examine the phylogeographic patterns exhibited by two sympatric species of surface and cave-dwelling peracarid crustaceans (Asellus aquaticus and Niphargus hrabei), and in doing so elucidate the possible roles of isolation and exaptation in the colonisation and successful adaptation to the cave environment.ResultsSpecimens of both species were sampled from freshwater hypogean (cave) and epigean (surface) habitats in Hungary, and additional data from neighbouring countries were sourced from Genbank. Sequencing of mitochondrial and nuclear loci revealed, through haplotype network reconstruction (TCS) and phylogenetic inference, the genetic structure, phylogeographic patterns, and divergence-time estimates of A. aquaticus and N. hrabei surface and cave populations. Contrasting phylogeographic patterns were found between species, with A. aquaticus showing strong genetic differentiation between cave and surface populations and N. hrabei lacking any evidence of genetic structure mediated by the cave environment. Furthermore, N. hrabei populations show very low levels of genetic differentiation throughout their range, which suggests the possibility of recent expansion events over the last few thousand years.ConclusionsIsolation by cave environment, rather than distance, is likely to drive the genetic structuring observed between immediately adjacent cave and surface populations of A. aquaticus, a predominantly surface species with only moderate exaptations to subterranean life. For N. hrabei, in which populations exhibit a fully ‘cave-adapted’ (troglomorphic) phenotype, the lack of genetic structure suggests that subterranean environments do not pose a dispersal barrier for this surface-cave species.

Comparing growth in surface and cave morphs of the species Astyanax mexicanus: insights from scales

BackgroundLife in the darkness of caves is accompanied, throughout phyla, by striking phenotypic changes including the loss or severe reduction in eyes and pigmentation. On the other hand, cave animals have undergone constructive changes, thought to be adaptive, to survive in this extreme environment. The present study addresses the question of the evolution of growth in caves, taking advantage of the comparison between the river-dwelling and the cave-dwelling morphs of the Mexican tetra, Astyanax mexicanus.ResultsA sclerochronology approach was undertaken to document the growth of the species in these two very distinct habitats. Scales from 158 wild Astyanax mexicanus specimens were analyzed from three caves (Pachón, Tinaja and Subterráneo) and two rivers (Rio Gallinas and Arroyo Lagarto) in San Luis Potosi and Tamaulipas, Mexico. A 10–13% reduction in scales size was observed in the cave morphs compared to the surface morphs. Age could be reliably inferred from annual growth increments on the scales from the two morphs of the species. Further comparisons with growth curves in laboratory conditions, obtained using the von Bertalanffy growth model, were also performed. In the wild and in the laboratory, cavefish originating from the Pachón cave reached smaller sizes than surface fish from three different locations: Rio Gallinas and Arroyo Lagarto (wild sampling) and Texas (laboratory population), respectively. Wild Pachón cavefish also seemed to grow to smaller sizes than the two other wild cavefish populations studied, Tinaja and Subterráneo. Finally, growth in the laboratory was faster than in the wild, particularly in the two first years of life.ConclusionsThese data suggest that cavefish originating from the Pachón cave are subjected to an intrinsic limitation of their final size, which is at least in part independent from energy/food availability. This growth limitation may be an advantageous way of limiting energy expenditure and food needs in the cave environment. Moreover, growth regulation evolved differently in independently evolved cave populations. These results are discussed with regard to the sources of energy or general ecological conditions present in caves, and to the differences in behavior or feeding skills known in cavefish.

Melanization in response to wounding is ancestral in arthropods and conserved in albino cave species

Many species adapted to aphotic subterranean habitats have lost all body pigmentation. Yet, melanization is an important component of wound healing in arthropods. We amputated appendages in a variety of cave-adapted and surface-dwelling arthropods. A dark clot formed at the site of injury in most species tested, including even albino cave-adapted species. The dark coloration of the clots was due to melanin deposition. The speed of wound melanization was uncorrelated with a difference in metabolic rate between surface and cave populations of an amphipod. The chelicerate Limulus polyphemus, all isopod crustaceans tested, and the cave shrimp Troglocaris anophthalmus did not melanize wounds. The loss of wound melanization in T. anophthalmus was an apomorphy associated with adaptation to subterranean habitats, but in isopods it appeared to be a symplesiomorphy unrelated to colonization of subterranean habitats. We conclude that wound melanization i) is an important part of innate immunity because it was present in all major arthropod lineages, ii) is retained in most albino cave species, and iii) has been lost several times during arthropod evolution, indicating melanization is not an indispensable component of wound healing in arthropods.

The transcriptomes of cave and surface populations of Gammarus minus (Crustacea: Amphipoda) provide evidence for positive selection on cave downregulated transcripts.

Gammarus minus, a freshwater amphipod living in the cave and surface streams in the eastern USA, is an excellent model for investigating evolutionary adaptation to the subterranean environment. RNA-Seq was conducted on one pair of morphologically distinct sister populations inhabiting surface and cave habitats to identify genes that were differentially expressed in the two populations, as well as to compare levels and patterns of genetic variation within and between populations. Of the 104,630 transcripts identified in the transcriptome assembly, 57% had higher average levels of expression in the cave population. After Benjamini-Hochberg correction for multiple tests, 1517 and 551 transcripts were significantly upregulated or downregulated, respectively, in the cave population, indicating an almost three-fold enrichment of cave-upregulated genes. The average level of nucleotide diversity across all transcripts was significantly lower in the cave population. Within the cave population, where the average nucleotide diversity of cave-downregulated transcripts was 75% that of the cave-upregulated transcripts, a highly significant difference, whereas within the spring population the nucleotide diversities of cave-downregulated and cave-upregulated transcripts was virtually identical. Three lines of evidence suggest that the reduced variation in cave downregulated transcripts is due to positive selection in the cave population: 1) the average neutrality index of cave-downregulated genes was < 1, consistent with positive selection, and significantly less than that of cave-upregulated genes; 2) Tajima’s D was positively correlated with the cave:surface expression ratio, and 3) cave-downregulated transcripts were significantly more likely to be highly diverged from their surface homologs than cave-upregulated transcripts. Five transcripts had fixed premature termination codons in the cave population. The expression patterns and sequence variation in one such transcript, encoding the DNA repair protein photolyase, were examined in more detail and provide the first evidence for the relaxation of functional constraint in this light-dependent protein in a subterranean population.

Homeostatic and circadian mechanisms of bioluminescence regulation differ between a forest and a facultative cave species of glowworm, Arachnocampa

Glowworms, members of the keroplatid fly genus, Arachnocampa, glow to attract prey. Here we describe substantial differences in the bioluminescence regulatory systems of two species; one is a troglophile with populations both in caves and outside of caves in wet forest (Arachnocampa tasmaniensis) and the other has no known cave populations (Arachnocampa flava). We find that A. tasmaniensis is ready to initiate bioluminescence at any time darkness is encountered. In contrast, A. flava shows a homeostatic control of bioluminescence; it is unlikely to initiate bioluminescence when exposed to dark pulses during the photophase and it does so with a long latency. Another difference between the two species is that A. tasmaniensis individuals synchronize their bioluminescence in the dark zone of caves under the control of the circadian system and A. flava individuals do not synchronize to each other, rather their circadian control system entrains to the light:dark cycle to promote nocturnal bioluminescence. Consequently, we produced a phase-response curve in response to photic entrainment under constant darkness for both species. The shape of the phase-response curves differs between the two species as does the overall sensitivity to the identical entrainment conditions. The phase-response curve of A. tasmaniensis facilitates synchronization whereas that of A. flava facilitates nocturnal glowing. The two-species comparison highlights possible pathways of divergence of circadian control of physiological functions that could be associated with the extreme ecological differences experienced in cave and surface habitats.

Diet comparison between rainforest and cave populations of Craugastor alfredi (Anura: Craugastoridae): does diet vary in contrasting habitats?

ABSTRACTInformation about interpopulational variation of diet is important for thoroughly understanding the ecological niche of a species, the possible attributes that have allowed it to live in different habitats and ecosystems (if it is the case) and the degree of dietary specialization. This study compared dietary composition and diversity, size of prey consumed and feeding intensity between two geographically proximate populations of Craugastor alfredi, inhabiting contrasting habitats: one located in a remnant tropical rainforest and the other population located within a cave entrance, in eastern Mexico. A total of 118 frogs (50 from rainforest and 68 from cave) were stomach-flushed and, from those, 86 had at least one prey item (42 from rainforest and 44 from cave). Consumption proportions of orthopterans differed between habitats, with frogs from the cave having higher importance values of this prey than frogs from the rainforest. Additionally, both dietary diversity and feeding intensity were higher in the rainforest population. It was concluded that the generalized diet of C. alfredi, besides the high consumption of orthopterans by the cave population, may have contributed to its success in cave entrances. Nonetheless, other non-feeding attributes like small body size, direct development and semiarboreality may also facilitate the use of rock crevices in caves for foraging and reproduction.

Characterization and comparison of activity profiles exhibited by the cave and surface morphotypes of the blind Mexican tetra, Astyanax mexicanus

Departure from normal circadian rhythmicity and exposure to atypical lighting cues has been shown to adversely affect human health and wellness in a variety of ways. In contrast, adaptation to extreme environments has led many species to alter or even entirely abandon their reliance upon cyclic environmental inputs, principally daily cycles of light and darkness. The extreme darkness, stability and isolation of cave ecosystems has made cave-adapted species particularly attractive systems in which to study the consequences of life without light and the strategies that allow species to survive and even thrive in such environments. In order to further explore these questions, we have assessed the rhythmicity of locomotion in the blind Mexican tetra, Astyanax mexicanus, under controlled laboratory conditions. Using high-resolution video tracking assays, we characterized patterns in locomotor activity and spatial tank usage for members of the surface and Pachón cave populations. Here we demonstrate that cavefish have a higher overall level of activity and use the space within the trial tank differently than surface fish. Further, Pachón cavefish show circadian rhythmicity in both activity and spatial tank usage under a 12:12 light/dark cycle. We provide further evidence that these cavefish retain a weakly light-entrainable, endogenous circadian oscillator with limited capability to sustain rhythms in activity, but not spatial tank usage, in the absence of photic cues. Finally, we demonstrate a putative behavioral “masking effect” contributing to behavioral rhythms and provide evidence that exposure to constant darkness during development may alter behavioral patterns later in life.

Investigating gene flow between the blind cavefish Garra barreimiae and its conspecific surface populations

Cave-dwelling taxa often share the same phenotypic modifications like absence of eyes and pigmentation. These “troglomorphic characters” are expressed in the populations of Garra barreimiae from the Al Hoota Cave and nearby Hoti Pit in Northern Oman. Surface morphotypes of this cyprinid species are common throughout the distribution area. Very rarely individuals with intermediate phenotypes can be found. In the present study, potential gene flow between cave and surface populations was tested and population structure within five sampling sites was assessed. Overall, 213 individuals were genotyped at 18 microsatellite loci. We found that the cave populations have lower genetic diversity and are clearly isolated from the surface populations, which seem to be sporadically in contact with each other. The results indicate a recent genetic bottleneck in the cave populations. Thus, it can be assumed that during climatic changes the connection between cave and surface water bodies was disjoined, leaving a subpopulation trapped inside. Nevertheless, occasional gene flow between the morphotypes is detectable, but hybridisation seems only possible in cave habitat with permanent connection to surface water. Individuals from surface sites bearing intermediate phenotypes but cave genotypes imply that phenotypic plasticity might play a role in the development of the phenotype.

Estimation of apparent survival probability of the harvestman Paranemastoma sillii sillii (Herman, 1871) from two caves

Reliable estimates of population parameters are lacking for most cave-dwelling species. This lack of knowledge may hinder the appropriate management of caves and populations of cave-dwelling species. Using monthly capture-recapture data and Cormack-Jolly-Seber models, we (i) estimated the apparent survival of individuals in two cave populations of the harvestman Paranemastoma sillii sillii (Herman, 1871) from the Mehedinti Mountains in south-western Romania; (ii) investigated temporal variation in apparent survival; (iii) tested if surface weather conditions affect apparent survival of cave-dwelling harvestmen through their influence upon cave environmental conditions and (iv) tested for sex differences in apparent survival. Our results show that the apparent monthly survival estimates were high for both studied cave populations and there was a significant sex effect on survival. Males had lower survival than females, and the survival difference between caves was larger in males than in females. Temporal (i.e., monthly) variation in apparent survival was low and the weather conditions at the surface had little influence on apparent survival as the environment inside the caves is well buffered against weather fluctuations outside the caves. Our results indicate that caves stabilize survival of facultative cave-dwelling species and may serve as microrefugia for epigean species. We suggest that caves should be considered for conservation because they may serve as a refuge for some epigean species during harsh weather conditions.

Genetic studies on the prehispanic population buried in Punta Azul cave (El Hierro, Canary Islands)

The aim of this study was to establish the genetic studies of the population from one of the most important known aboriginal funerary spaces of the island of El Hierro (Canary Islands), the Punta Azul cave, which harbors remains of 127 individuals. Sixty-one adult tibiae were examined, 32 left and 29 right. Radiocarbon dating yields an antiquity of 1015–1210 AD. We have obtained an overall success rate of 88.5% for the molecular sexing, and of 90.16% for the uniparental markers. Short tandem repeats (STR) profiles were also possible for 45.9% of the samples. This performance is a consequence of the good conservation of the bones in their archaeological context. The mtDNA composition of the sample is characterized by the complete fixation of the H1-16260 lineage. These results can be explained by a mixture of consecutive founding events, a bottleneck episode at the beginning of the colonization and/or as a consequence of genetic drift. Paternal lineages were also affected by these processes but in a less acute way. These differences lead us to propose social behaviors as an explanation for this difference. The maternal transmission of the lineages, mentioned in ethnohistorical sources of the Archipelago, could be an explanation. These results could be in agreement with endogamous practices, but the autosomal STR results indicate a relative high diversity. These results have allowed us to characterize the Punta Azul cave population and see the way in which geographical isolation, the process of adaptation and specific social behaviors affected the aboriginal population of the Island.

Parallel evolution evidenced by molecular data in the banded-tetra (Astyanax fasciatus)

Astyanax is well known as a model for developmental biology studies, particularly with regard to Mexico's cave populations. More than 130 species of Astyanax are already known, most of which live in South America. The occurrence of cryptic species and species complexes elucidated by chromosomal and genetic studies demonstrates that the relationship between morphology and molecular evolution is quite complex within this group. In this work, we demonstrate that morphology does not follow the path of vicariant processes observed in Astyanax fasciatus populations, which separated about three million years ago, although molecular data suggests its separation in two species.