Population size and time since island isolation determine genetic diversity loss in insular frog populations

Abstract

Understanding the factors that contribute to loss of genetic diversity in fragmented populations is crucial for conservation measurements. Land-bridge archipelagoes offer ideal model systems for identifying the long-term effects of these factors on genetic variations in wild populations. In this study, we used nine microsatellite markers to quantify genetic diversity and differentiation of 810 pond frogs (Pelophylax nigromaculatus) from 24 islands of the Zhoushan Archipelago and three sites on nearby mainland China and estimated the effects of the island area, population size, time since island isolation, distance to the mainland and distance to the nearest larger island on reduced genetic diversity of insular populations. The mainland populations displayed higher genetic diversity than insular populations. Genetic differentiations and no obvious gene flow were detected among the frog populations on the islands. Hierarchical partitioning analysis showed that only time since island isolation (square-root-transformed) and population size (log-transformed) significantly contributed to insular genetic diversity. These results suggest that decreased genetic diversity and genetic differentiations among insular populations may have been caused by random genetic drift following isolation by rising sea levels during the Holocene. The results provide strong evidence for a relationship between retained genetic diversity and population size and time since island isolation for pond frogs on the islands, consistent with the prediction of the neutral theory for finite populations. Our study highlights the importance of the size and estimated isolation time of populations in understanding the mechanisms of genetic diversity loss and differentiation in fragmented wild populations.

Genetic variation of the striped hamster (Cricetulus barabensis) and the impact of population density and environmental factors

“…As shown in Figure 2, an obvious correlation can be inferred between the levels of genetic diversity and the population density. Our results are in accordance with studies in other species in which a similar correlation was found (Aspi et al 2006;Berthier et al 2006;Eckert et al 2008;Frankham 1996;Furlan et al 2012;Montgomery et al 2000;Wang et al 2013), including other rodents (Krebs 2013) and hamster species (Romanenko et al 2007), like the greater longtailed hamster (Dong et al 2010;Xie and Zhang 2006;Xu et al 2013a;Xue et al 2014), the golden hamster (Karsten et al 2005), and the common hamster (Banaszek et al 2012;Neumann et al 2005). Similarly, the genetic diversity of the striped hamster has experienced a trend of continuous decline in recent years.…”

A comparative study on genetic effects of artificial and natural habitat fragmentation on Loropetalum chinense (Hamamelidaceae) in Southeast China

“…These findings contrast with recent studies in either region, indicating that recent artificial 'islanding' in the TIL region can lead to significant loss of genetic diversity, especially in short-lived herbs (Yuan et al, 2012). Moreover, in the Zhoushan Archipelago, it was recently demonstrated that overwater distance is a significant barrier to contemporary gene flow in both pond frogs (Wang et al, 2014) and fig wasps (Liu et al, 2013), whereby in either instance genetic drift following Holocene island formation likely decreased diversity and increased differentiation among insular populations. By contrast, this study on L. chinense is the first to highlight the importance of gene flow (most likely via seed) in sustaining genetic diversity and preventing inter-population differentiation in the face of habitat 'insularization' in both the TIL region and the Zhoushan Archipelago, that is, at different temporal and spatial scales.…”

“…This hypothesis is further suggested by the fact that the natural landscapes of the Zhoushan Archipelago have been greatly modified by human activities over the last 20 years, whereby the impervious surface area continues to increase at an average rate of 1.97 km 2 per year . Although certain agricultural developments also may have positive effects for some organisms, for example, frogs, for which irrigated fields provide suitable habitats (Knutson et al, 2004;Wang et al, 2014), much of the natural vegetation cover (that is, subtropical evergreen broad-leaved forest) has now been destroyed . Evidently, more finescale studies, using precise deforestation records, highly resolving molecular (for example, genomics) approaches, and a dense sampling, are required to determine whether such recent forest fragmentation has already affected the genetic architecture of constituent species, such as L. chinense.…”

“…However, levels of genetic variability can also recover due to rapid post-bottleneck population growth (Nei et al, 1975) or even small amounts of immigration (Keller et al, 2001). Moreover, levels of genetic diversity in post-fragmentation populations are also highly influenced by life-history traits, in particular longevity and mating system (Kuo and Janzen, 2004;Hailer et al, 2006) and characteristics of the landscape (Wang et al, 2014). For example, long generation times slow the effective rate of genetic drift if habitat fragmentation has occurred only recently (for example, o200 years ago), thus providing an 'intrinsic buffer' to the loss of genetic diversity (Hailer et al, 2006).…”

“…These islands represent former hilltops that were not flooded by the lake. Although there are numerous studies of genetic diversity on landbridge islands in America (Jordan and Snell, 2008;Barker et al, 2012;Bell et al, 2012), Australia (Furlan et al, 2012;Stankowski and Johnson, 2014) and the Mediterranean Basin (Bittkau and Comes, 2005), relatively little attention has been paid to China (Liu et al, 2013;Wang et al, 2014), despite the fact that China has 410 000 islands, with climates ranging from tropical to cold temperate conditions (Committee ZGHDZ, 2013).…”