Genetic drift and rapid evolution of viviparity in insular fire salamanders (Salamandra salamandra)

Abstract

Continental islands offer an excellent opportunity to investigate adaptive processes and to time microevolutionary changes that precede macroevolutionary events. We performed a population genetic study of the fire salamander (Salamandra salamandra), a species that displays unique intraspecific diversity of reproductive strategies, to address the microevolutionary processes leading to phenotypic and genetic differentiation of island, coastal and interior populations. We used eight microsatellite markers to estimate genetic diversity, population structure and demographic parameters in viviparous insular populations and ovoviviparous coastal and interior populations. Our results show considerable genetic differentiation (F ST range: 0.06-0.27), and no clear signs of gene flow among populations, except between the large and admixed interior populations. We find no support for island colonization by rafting or intentional/accidental anthropogenic introductions, indicating that rising sea levels were responsible for isolation of the island populations approximately 9000 years ago. Our study provides evidence of rapid genetic differentiation between island and coastal populations, and rapid evolution of viviparity driven by climatic selective pressures on island populations, geographic isolation with genetic drift, or a combination of these factors. Studies of these viviparous island populations in early stages of divergence help us better understand the microevolutionary processes involved in rapid phenotypic shifts.

Vicariance and marine migration in continental island populations of a frog endemic to the Atlantic Coastal forest

“…Therefore, the general assumption is that island populations of amphibians are completely isolated at the time of vicariance during formation of continental islands (Richards and Moore, 1996;Brown and Guttman, 2002). This isolation scenario seems to hold for some continental island dwelling amphibians: a recent study of fire salamanders showed a reduction of genetic diversity on insular populations indicating that these populations evolved in isolation without any subsequent marine dispersal events (Velo-Antón et al, 2012). However, some studies indicate that amphibians are in fact able to disperse to islands (Seppa and Laurila, 1999;Evans et al, 2003;Vences et al, 2003), although the exact mechanism of dispersal is unknown.…”

“…However, more recently studies have also focused on taxa inhabiting continental islands (Gill, 1980;Bittkau and Comes, 2005;Jordan and Snell, 2008;Velo-Antón et al, 2012). In contrast to oceanic islands that are formed de novo by volcanic activity, continental islands were once continuous with continental landmasses and are formed by sea level changes that isolate the highest points on the edge of the continental shelf.…”

“…Similarly, islands that are more distant from the coast should receive fewer migrants and less influx of genetic diversity. Therefore, the effects of drift will be intensified when founding populations are small, when islands are small in area and when islands are far from the mainland source population (Jaenike, 1973;Frankham, 1997;Clegg et al, 2002a;Velo-Antón et al, 2012).…”

Did postglacial sea-level changes initiate the evolutionary divergence of a Tasmanian endemic raptor from its mainland relative?

“…The Tasmanian population of A. audax became isolated very recently from the mainland population, contrary to the paradigm of marine transgression-induced vicariance of continental island populations [12,37,55]. Coalescent estimates employing 'conventional' avian mitochondrial substitution rates suggest divergence 3-95 years ago.…”

“…Taiwan, Indonesia, New Guinea, Sri Lanka, Britain), their divergence from those on the adjacent mainland has received somewhat less attention than those of oceanic islands. Divergences of continental island biotas are often assumed to reflect vicariant isolation from the adjacent mainland during the marine transgression that followed the LGM (figure 1a), without full consideration of alternative hypotheses [12]. Even if divergence was initiated by the most recent marine transgression, divergence may have continued under gene flow in taxa with marine dispersal capability ( [13]; figure 1b).…”