Parallels between two geographically and ecologically disparate cave invasions by the same species,Asellus aquaticus(Isopoda,Crustacea)

Abstract

Caves are long-known examples of evolutionary replications where similar morphologies (troglomorphies) evolve independently as the result of strong natural selection of the extreme environment. Recently, this paradigm has been challenged based on observations that troglomorphies are inconsistent across taxa and different subterranean habitats. We investigated the degree of replicated phenotypic change in two independent cave invasions by the freshwater isopod Asellus aquaticus; the first in a sulphidic aquifer in Romania, the second in a sinking river in the Dinaric Karst in Slovenia. Both ancestral surface populations still live alongside the subterranean ones. Phylogenetic analyses show independence of the two colonization events, and microsatellite analysis shows no evidence of ongoing genetic exchange between surface and subterranean ecomorphs. The overall morphology has changed dramatically at both sites (50 of 62 morphometric traits). The amount of phenotypic change did not reflect differences in genetic diversity between the two ancestral populations. Multivariate analyses revealed divergent evolution in caves, not parallel or convergent as predicted by the current paradigm. Still, 18 traits changed in a parallel fashion, including eye and pigment loss and antennal elongation. These changes might be a consequence of darkness as the only common ecological feature, because Romanian caves are chemoautotrophic and rich in food, whereas Slovenian caves are not. Overall, these results show that morphologically alike surface populations can diverge after invading different subterranean habitats, and that only about one-third of all changing traits behave as troglomorphies in the traditional sense.

Neuronal Regression of Internal Leg Vibroreceptor Organs in a Cave-Dwelling Insect (Orthoptera: Rhaphidophoridae: <b><i>Dolichopoda araneiformis</i></b>)

“…Sensory structures which convey a weakened or lost selective advantage usually deteriorate over evolutionary time [Wilkens et al, 1979;Fong et al, 1995]. Such regressive evolution of sensory structures in general has several likely causes, including negative selection due to metabolic costs, genetic drift, or both [Niven and Laughlin, 2008;Christiansen, 2012;Rétaux and Casane, 2013;Konec et al, 2015]. The selective advantage was apparently lost only for the SGO and the AO in D. araneiformis , which underwent a substantial loss of sensilla, while the IO may have remained unaffected.…”

“…While vision, pigmentation, and wings in arthropods are often lost or reduced, other senses like chemoreception and touch become more elaborate, typically accompanied by elongation of the appendages Turk et al, 1996;Bland et al, 1998;Bell et al, 2007;Protas et al, 2011;Konec et al, 2015]. While mechanosensory systems like the lateral line in fishes can also become more prominent [Yoshizawa et al, 2010[Yoshizawa et al, , 2014Protas and Jeffery, 2012], the evolutionary effect of the cave environment on the sensory organs detecting substrate vibrations is less well studied.…”

Comparative study of acetylcholinesterase and glutathione S-transferase activities of closely related cave and surface Asellus aquaticus (Isopoda: Crustacea)

“…It inhabits various freshwater habitats throughout most of Europe, including caves [1], [2]. The species exhibits strong genetic structuring in the southern and eastern part of its range [3], [4], [5]. Genetically distinct cave populations that resulted from polytopic and polychronous immigration to the cave environment still have their surface counterparts [4], [6], [7].…”

“…The species exhibits strong genetic structuring in the southern and eastern part of its range [3], [4], [5]. Genetically distinct cave populations that resulted from polytopic and polychronous immigration to the cave environment still have their surface counterparts [4], [6], [7]. Pairs of surface and cave populations have gained increasing recognition as a model system to address questions of evolutionary parallelism and convergence [8], [9], [10].…”

The troglomorphic adaptations of Namanereidinae (Annelida, Nereididae) revisited, including a redescription of Namanereis cavernicola (Solís-Weiss &amp; Espinasa, 1991), and a new Caribbean species of Namanereis Chamberlin, 1919

“…In an ecological classification, obligate residents of subterranean habitats are called troglobionts, and specifically stygobionts if they live in aquatic systems; interestingly, not all organisms living in subterranean environments are troglomorphs, nor are all organisms showing troglomorphic features are troglobionts (Sket 2008, Culver and Pipan 2009b, Pipan and Culver 2012, Konec et al 2015. The fact that troglomorphic features are present in species living in non-cave environments indicates that their evolution is more complex than supposed (Heads 2010); therefore, the assumption of features as troglomorphic just because some morphologically modified species have current subterranean distributions deserves critical attention.…”