Outbreeding depression in the common frog, Rana temporaria

Abstract

Theory suggests that parental relatedness is a continuous variable with a fitness optimum that we heretoforth will refer to as 'optimal outbreeding'. In the present paper, we test this proposition from a conservation (translocation) perspective. Amphibians are facing a global decline and many amphibian populations are today small and threatened by extinction. Because genetic differentiation is often high between amphibian populations, they could be particularly sensitive to outbreeding depression, e.g. due to breakdown of locally adapted gene complexes. We tested if outbreeding would reduce fitness in common frogs, Rana temporaria, crossed from a large and an isolated, small population, separated by 130 km, using artificial fertilization. For females from the large population, tadpoles were significantly smaller and more malformed in crosses with males from the small population, than with males from the large population. For the small population, however, no significant paternal genetic effects could be found. The difference in response to outbreeding between populations was accompanied with significant differences in the importance of maternal effects. We conclude that care should be taken when translocating frogs between distantly related populations to avoid outbreeding depression.

Global Amphibian Declines, Loss of Genetic Diversity and Fitness: A Review

“…This study suggests that the fungus attacks a variety of genotypes indiscriminately, but also that severe outbreeding can have a negative effect on individual resistance to the disease. The latter result is perhaps not surprising, since other negative outbreeding effects, in terms of larval malformations and size, have been documented even within the same ranid species in crosses between two populations separated by just 130 km [89].…”

“…This is commonly explained by a dependence on moist habitats and slow terrestrial movement capabilities [84,85]. Although these limitations are clearly not true for all amphibians and should not be accepted by default [86,87], it is not unreasonable to use this generalisation when comparing amphibian migration rates [88] or levels of inter-population genetic differentiation (e.g., [47,89]), with that of other vertebrates. Consequently, many amphibian sub-populations might be prone to high, background genetic drift because of limited connectivity, causing a state of natural fragmentation of the gene pool.…”

Beyond the point of no return? A comparison of genetic diversity in captive and wild populations of two nearly extinct species of Goodeid fish reveals that one is inbred in the wild

“…Indeed, outcrossing may be detrimental for naturally inbred populations (e.g. outcrossed inbred males produce malformed tadpoles in Rana temporaria; Sagvik et al, 2004), particularly when they are outcrossed with captive populations, as demonstrated by the loss, rather than gain of genetic diversity in the Western mosquito fish, Gambusia affinis following the release of fish from captive stocks (Stockwell et al, 1996). There is also evidence from captive studies that establishing populations from multiple stocks can lead to outbreeding depression in the related G. holbrooki (Leberg, 1993).…”

Genetic diversity of Broussonetia papyrifera populations in southwest China

“…Third, the manual transfer of mature seeds and artificial pollination among populations can enhance the gene flow. Taking into account the observation that B. papyrifera populations are highly structured genetically, outbreeding depression might be a potential genetic threat for already weakened populations (Sagvik et al, 2005). Therefore, it may be wise to protect a network of populations that exchange genetic material and are able to reinforce each other (Rodrigues et al, 2013).…”