Patterns of gene flow and genetic structure in cave-dwelling crickets of the Tuscan endemic, Dolichopoda schiavazzii (Orthoptera, Rhaphidophoridae)

Abstract

Dolichopoda schiavazzii is a cave cricket species endemic to Tuscany, Italy. This species inhabits natural limestone caves and also man-made hypogean environments. Dolichopoda schiavazzii can colonize new environments both passively and actively. This species shows a metapopulational structure depending on both the cave's external bioclimatic conditions and the geographical distance. This paper reports data on 26 allozyme loci in nine populations of D. s. schiavazzii and in one of D. s. caprai, investigates their genetic structuring and provides measures of gene flow between them at different geographical scales. Some loci showed heterozygote deficiencies, probably owing to the Wahlund effect, caused by the mixing of individuals belonging to two different cohorts. Genetic subdivision is high, particularly among populations inhabiting caves located on the Tyrrhenian coast. The mean FST (0 estimator) across populations was 0.34. An analysis of the gene flow levels, carried out by comparing pairwise Nm values, indicates that the number of migrants drops as the geographical distance increases, suggesting the actual occurrence of gene flow only between geographically close populations in an inner area of Tuscany where the occurrence of mesophilous woods might favour migration between caves. The general picture, however, is one of a substantial lack of gene flow, even if a significant trend of isolation by distance is found, probably reflecting historical gene flow.

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

“…Molecular data provide new insights into the levels of species diversity in cave systems. Historically, allozyme genetic divergence data permitted the discrimination of geographically distant cave populations and the possible occurrence of cryptic species (Cesaroni et al 1981;Sbordoni et al 1981;Kane et al 1992;Allegrucci et al 1997). Subsequent advances in sequencing technology have led to the use of DNA sequence data for the identification of cryptic species (e.g.…”

Genetic Variation and Population Structure of Oriental Migratory Locust, Locusta migratoria manilensis, in China by Allozyme, SSRP-PCR, and AFLP Markers

“…In our study, the eight L. m. manilensis populations show an overall heterozygote deficiency, which results in significant Hardy-Weinberg disequilibrium. This deviation has also been observed in other Orthoptera species (Allegrucci et al, 1997;Orr et al, 1994). Heterozygote deficiency can be the consequence of several factors, including inbreeding, nonrandom mating, bottleneck effects, and parthenogenesis (Hong and Ando, 1998).…”

“…The insignificant overall F st (F st = 0.026, P > 0.05) and the lesser genetic distance (D not shown) obtained by the allozyme method suggest overall little genetic divergence among these eight populations and a nearly uniformly distributed genetic structure. This datum (F st = 0.026) was smaller than in the populations of the Chinese rice grasshopper, Oxya chinensis (0.051; ; the cave cricket, Dolichopoda schiavazzii (0.34; Allegrucci et al, 1997); Melanoplus sanguinipes in California (0.449; Orr et al, 1994); and Ephippiger ephippiger (Oudman et al, 1990). All of these data suggest that local populations of nonmigratory insects of the Orthoptera tend to be strongly differentiated.…”

Comparative phylogeography of two codistributed subgenera of cave crickets (Orthoptera: Rhaphidophoridae: Ceuthophilus spp.)

“…For example, Caccone & Sbordoni (1987) generally found low rates of gene flow between populations of cave dependent Hadenoecus crickets, but they also noted that populations in regions with continuous and highly fissured limestone features were less genetically differentiated in comparison to higher levels of differentiation found between populations in regions where the limestone distribution was more fragmented. In general, molecular genetic studies of cave-adapted organisms have uncovered high levels of genetic differentiation (Hedin, 1997;Strecker et al, 2003;Snowman et al, 2010), cryptic diversification (Lef ebure et al, 2006;Niemiller et al, 2012), and genetic variation structured by geographical and geological features (Allegrucci et al, 1997;Allegrucci et al, 2005). However, there are also cases where there is evidence of some recent dispersal between caves (Rivera et al, 2002;Ketmaier et al, 2013;Lef ebure et al, 2006) tied to ecological characteristics of the species being studied or geological connections between caves (Moulds et al, 2007).…”