Speciation in killifish and the role of salt tolerance

Abstract

Species pairs whose distributions are tied to environmental conditions provide intriguing candidates for the study of ecological speciation. Here, we examine the role that adaptation to salinity has played in the divergence between two closely related species, Lucania goodei and Lucania parva, whose distributions reflect salinity (L. goodei– fresh water, L. parva– euryhaline). We first tested whether these two species display local adaptation and, subsequently, tested for ecological, genic and behavioural isolation by performing crosses within and between L. goodei and L. parva and raising offspring under various salinities. We found strong evidence for differential adaptation to salinity and also for behavioural isolation where animals preferentially mated with conspecifics over heterospecifics. However, we found no evidence for F1 hybrid inviability. We discuss the general lack of evidence for genic isolation in teleost fish and whether this is a real phenomenon or simply a reflection of experimental design.

Genetic Diversity and Population History of the Endangered Killifish Aphanius baeticus

“…Previous studies in killifish species with similar habitat requirements to those of A. baeticus (i.e., coastal and high-salinity water bodies) showed striking differences in mitochondrial and nuclear genetic distribution, shifting from high to low genetic variability (Maltagliati et al 2003;Whitehead 2009;Angeletti et al 2010;Tatarenkov et al 2011;Ferrito et al 2013). Consequently, it has been argued that these differences in genetic variability patterns are not only determined by habitat adaptation but also by specific life-history traits and historical processes (Fuller et al 2007;Whitehead 2009;Strand et al 2012). Overall, the detected mtDNA genetic variability was low in relation to other nonthreatened killifish species (e.g., A. fasciatus; Rocco et al 2007;Pappalardo et al 2008;Ferrito et al 2013).…”

Postzygotic Isolation Evolves before Prezygotic Isolation between Fresh and Saltwater Populations of the Rainwater Killifish,Lucania parva

“…Multiple lines of evidence suggest that adaptation to different salinity conditions has occurred between species. L. goodei has higher fitness in fresh water relative to L. parva , and L. parva fares better in brackish and salt water than L. goodei [41]. Additionally, L. goodei has a decreased rate of hatching success at high salinities while L. parva has a lower rate of survival to adulthood in fresh water [41–43].…”

“…Behavioral isolation is quite strong with L. parva and L. goodei mating pairs taking longer to produce eggs than conspecific pairs and producing fewer eggs [41]. Postzygotic isolation between species is both extrinsic and intrinsic.…”

Insight Into Genomic Changes Accompanying Divergence: Genetic Linkage Maps and Synteny ofLucania goodeiandL. parvaReveal a Robertsonian Fusion

“…Lucania goodei is found primarily in freshwater habitats, whereas L. parva is euryhaline and can be found in fresh, brackish, and marine habitats (Lee et al 1980). Survival at various life stages differs between Lucania species in different salinities (Fuller et al 2007; Fuller 2008). Lucania goodei and L. parva also show divergence in sequence and expression of a number of salinity tolerance genes (Berdan and Fuller 2012; Kozak et al 2014).…”