Rapid adaptive phenotypic change following colonization of a newly restored habitat

Abstract

Real-time observation of adaptive evolution in the wild is rare and limited to cases of marked, often anthropogenic, environmental change. Here we present the case of a small population of reed warblers (Acrocephalus scirpaceus) over a period of 19 years (1996–2014) after colonizing a restored wetland habitat in Malta. Our data show a population decrease in body mass, following a trajectory consistent with a population ascending an adaptive peak, a so-called Ornstein–Uhlenbeck process. We corroborate these findings with genetic and ecological data, revealing that individual survival is correlated with body mass, and more than half of the variation in mean population fitness is explained by variation in body mass. Despite a small effective population size, an adaptive response has taken place within a decade. A founder event from a large, genetically variable source population to the southern range margin of the reed warbler distribution likely facilitated this process.

Anthropogenic habitat alteration leads to rapid loss of adaptive variation and restoration potential in wild salmon populations

“…Adaptive variation is likely important to the success of species restoration efforts (56,68). The planned removal of Klamath dams provides an opportunity to restore Chinook to historical habitat that is unprecedented in scale and provides a lens through which to evaluate the challenges of recovering the spring-run phenotype.…”

Inconclusive evidence for rapid adaptive evolution

“…Sætre et al 1 described a case of decreasing adult body mass in reed warblers ( Acrocephalus scirpaceus ) across a period of 19 years following the restoration of a marshland in Malta. This phenotypic change was interpreted as rapid adaptive evolution because body mass followed a trajectory consistent with that of a population ascending an adaptive peak (a so-called Ornstein–Uhlenbeck model), and correlated with estimates of population fitness and individual survival.…”

“…This phenotypic change was interpreted as rapid adaptive evolution because body mass followed a trajectory consistent with that of a population ascending an adaptive peak (a so-called Ornstein–Uhlenbeck model), and correlated with estimates of population fitness and individual survival. Sætre et al’s 1 study would thus constitute an example of exceptionally rapid adaptive evolution in the wild. However, we argue that their finding is most likely a result of the inclusion of fat and heavy migrants in the data set, which seriously inflated the average body mass during the first years of the study.…”

“…Greece 3 and Spain 4 ), which is comparable to Malta as it lies relatively close to the Mediterranean Sea and Sahara Desert. Therefore, to analyse body mass evolution, several factors need to be corrected for, but only diurnal variation was taken into account in Sætre et al’s 1 analysis. Their 1 data set includes birds caught from May to August, which encompasses not only the breeding season, but also the moulting period when the birds replace their body feathers (during which they are known to be heavier 5 , 6 ) and, importantly, also the spring (until mid-June) and autumn (from mid-July) migration periods when individuals from populations breeding north of Malta are passing the island on migration from and towards their African winter quarters.…”

“…Therefore, to analyse body mass evolution, several factors need to be corrected for, but only diurnal variation was taken into account in Sætre et al’s 1 analysis. Their 1 data set includes birds caught from May to August, which encompasses not only the breeding season, but also the moulting period when the birds replace their body feathers (during which they are known to be heavier 5 , 6 ) and, importantly, also the spring (until mid-June) and autumn (from mid-July) migration periods when individuals from populations breeding north of Malta are passing the island on migration from and towards their African winter quarters. Because the migration period is particularly extensive in this species 7 , it is only during a short period (mid-June to mid-July) when captures of unknown birds can be confidently assigned as local breeders.…”