Geographic variation and genetic relationships in populations of the \u3cem\u3eAndroniscus dentiger\u3c/em\u3e complex from Central Italy (Isopoda, Oniscidea, Trichoniscidae)

Androniscus dentiger is a terrestrial isopod distributed from Great Britain to North Africa, inhabiting humid edafic environments, superficial underground compartments and both natural and artificial caves. In this study allozyme data have been used to investigate the geographic variation and the genetic relationships of several populations of A. dentiger from Central Italy, using as outgroups populations from four congeneric species, A. calcivagus, A. cfr. subterraneus, A. spelaeorum, and A. degener. Multivariate analysis of A. dentiger allele frequencies indicates the existence of a group of populations (group A) distributed in a wide geographic area which are genetically slightly differentiated, and several populations (arbitrarily defined as group B) which show differentiation levels comparable to those observed between the morphologically well differentiated species. The low valley of the river Tiber seems to act as an effective geographic barrier between the populations from group A and the remaining ones. The genetic divergence between populations within the group A seems to have a recent origin. This is suggested by the low genetic distances and heterozygosity values within the group A, and by the very low number of private alleles occurring in this group. The high degree of intraspecific and interspecific genetic differentiation is not consistent with the levels of morphological differentiation traditionally used to distinguish different species within this genus. On the whole, these data suggest that A. dentiger might be considered as a complex of cryptic/sibling species

Geographic variation and genetic relationships in populations of the Androniscus dentiger complex from Central Italy (Isopoda, Oniscidea, Trichoniscidae)

Androniscus dentiger is a terrestrial isopod distributed from Great Britain to North Africa, inhabiting humid edafic environments, superficial underground compartments and both natural and artificial caves. In this study allozyme data have been used to investigate the geographic variation and the genetic relationships of several populations of A. dentiger from Central Italy, using as outgroups populations from four congeneric species, A. calcivagus, A. cfr. subterraneus, A. spelaeorum, and A. degener. Multivariate analysis of A. dentiger allele frequencies indicates the existence of a group of populations (group A) distributed in a wide geographic area which are genetically slightly differentiated, and several populations (arbitrarily defined as group B) which show differentiation levels comparable to those observed between the morphologically well differentiated species. The low valley of the river Tiber seems to act as an effective geographic barrier between the populations from group A and the remaining ones. The genetic divergence between populations within the group A seems to have a recent origin. This is suggested by the low genetic distances and heterozygosity values within the group A, and by the very low number of private alleles occurring in this group. The high degree of intraspecific and interspecific genetic differentiation is not consistent with the levels of morphological differentiation traditionally used to distinguish different species within this genus. On the whole, these data suggest that A. dentiger might be considered as a complex of cryptic/sibling species

Gene flow among populations of the troglophilic woodlouse Androniscus dentiger from central ltaly

In cave animals, different levels of gene flow among populations appear to be related to the degree of cave dependence of each organism (Caccone, 1985). In general, high degrees of cave dependence entail a reduced ability of organisms to survive in surface environments, which in turn strongly influences their dispersal ability. In nature, constraints for dispersal can be geographical and ecological.Sometimes barriers can be represented by fluvial barriers or drainage divides (Barr, 1985); in other cases, a non-continuous "superficial underground compartment" (Juberthie, 1980) may represent an ecological break in the routes for dispersal (Culver, 1982). The existence of morphological variation among cave populations is often interpreted as reflecting a reduction in gene flow across dispersal barriers. Sometimes, morphological and genetic data are congruent in indicating similar geographic variation patterns (Kane et al. , 1992). In other cases, these different sets of characters clash, revealing independent trends (Allegrucci et al., 1987). This fact may reflect the different weight of selective pressures: there is evidence that variation in these characters is related to the distribution of ecological factors, such as temperature (De Matthaeis et al., 1985; Sbordoni et al., 1991). On the other hand, local populations of cave-dwelling and endogean arthropods may be highly differentiated genetically without exhibiting corresponding morphological differentiation (Laing et al., 1976; Delay et al., 1980; Cobolli Sbordoni et al., 1980; Sbordoni, 1982). Thus variation in morpho1ogical features by itself is not a good predictor of the levels of gene flow among a group of cave populations. In these circumstances we studied a woodlouse, Androniscus dentiger (Isopoda, Oniscidea), inhabiting humid edaphic environments and both natural and artificial caves. In A. dentiger the occurrence of an appreciable geographical variation among populations is not revealed by any of the morphological characters examined so far. This species has a wide distribution, which may suggest the existence of gene flow among populations, especially between neighbours. To test this hypothesis, allozyme electrophoresis was carried out to investigate the genetic structure of 28 populations at 19 gene loci. Fst values indicate a high level of differentiation. Allozyme data were used to estimate levels of gene flow among populations. The methodological approach and the biologica! significance of the results obtained are discussed

Patterns of speciation in Dolichopoda cave crickets (Orthoptera, Rhaphidophoridae)

This study focuses on the phylogenetic relationships among ninety percent of known Dolichopoda species (44 out of 49); primarily a Mediterranean genus, distributed from eastern Pyrenees to Caucasus. A total of 2,490 base pairs were sequenced corresponding to partial sequences of one nuclear (28SrRNA) and three mitochondrial genes (12S, 16S and COI). A relaxed molecular clock, inferred from Bayesian analysis was applied to estimate the divergence times between the lineages using well dated palaeoevents of the study areas. Molecular substitution rates per lineage per million years were also obtained for each analysed gene. Based on the nearly complete species phylogeny, temporal patterns of diversification were analysed using Lineage-Through-Time plots and diversification statistics. Alternative hypotheses about the colonization of western Mediterranean by Dolichopoda species were tested by means of Approximate Bayesian Computation analysis and by comparing the degree of discordance between species trees and gene trees under four plausible biogeographic scenarios. Both phylogenetic reconstruction and results from the biogeographical hypotheses test suggested that the current distribution of Dolichopoda species has been essentially shaped from the palaeogeographic and climatic events occurred in the Mediterranean region, starting from Late Miocene up to the Plio-Pleistocene. Our results suggest that the current distribution of Dolichopoda can be explained by a combination of both vicariance and dispersal events, with many processes occurring in ancestral epigean populations before the invasion of the subterranean environment

Is Radon Emission in Caves Causing Deletions in Satellite DNA Sequences of Cave-Dwelling Crickets?

The most stable isotope of radon, 222Rn, represents the major source of natural radioactivity in confined environments such as mines, caves and houses. In this study, we explored the possible radon-related effects on the genome of Dolichopoda cave crickets (Orthoptera, Rhaphidophoridae) sampled in caves with different concentrations of radon. We analyzed specimens from ten populations belonging to two genetically closely related species, D. geniculata and D. laetitiae, and explored the possible association between the radioactivity dose and the level of genetic polymorphism in a specific family of satellite DNA (pDo500 satDNA). Radon concentration in the analyzed caves ranged from 221 to 26000 Bq/m3. Specimens coming from caves with the highest radon concentration showed also the highest variability estimates in both species, and the increased sequence heterogeneity at pDo500 satDNA level can be explained as an effect of the mutation pressure induced by radon in cave. We discovered a specific category of nuclear DNA, the highly repetitive satellite DNA, where the effects of the exposure at high levels of radon-related ionizing radiation are detectable, suggesting that the satDNA sequences might be a valuable tool to disclose harmful effects also in other organisms exposed to high levels of radon concentration