Human disturbance causes the formation of a hybrid swarm between two naturally sympatric fish species

Most evidence for hybrid swarm formation stemming from anthropogenic habitat disturbance comes from the breakdown of reproductive isolation between incipient species, or introgression between allopatric species following secondary contact. Human impacts on hybridization between divergent species that naturally occur in sympatry have received considerably less attention. Theory predicts that reinforcement should act to preserve reproductive isolation under such circumstances, potentially making reproductive barriers resistant to human habitat alteration. Using 15 microsatellites, we examined hybridization between sympatric populations of alewife (Alosa pseudoharengus) and blueback herring (A. aestivalis) to test whether the frequency of hybridization and pattern of introgression have been impacted by the construction of a dam that isolated formerly anadromous populations of both species in a landlocked freshwater reservoir. The frequency of hybridization and pattern of introgression differed markedly between anadromous and landlocked populations. The rangewide frequency of hybridization among anadromous populations was generally 0–8%, whereas all landlocked individuals were hybrids. Although neutral introgression was observed among anadromous hybrids, directional introgression leading to increased prevalence of alewife genotypes was detected among landlocked hybrids. We demonstrate that habitat alteration can lead to hybrid swarm formation between divergent species that naturally occur sympatrically, and provide empirical evidence that reinforcement does not always sustain reproductive isolation under such circumstances.     

Seasonal variations in fat content and fatty acid composition of male and female coregonid' bondella' from Lake Maggiore and landlocked shad from Lake Como (Northern Italy)

The Lake Maggiore bondella Coregonus macrophthalmus use perivisceral adipose tissue for gonadal development (with particular evidence in females), and muscle fat as an energy source. Females use mainly saturated fatty acids (SFA) for energy purposes, while males use monounsaturates (MUFA) also. During vitellogenesis, females can also mobilize fatty acid precursors of gonadal highly unsaturated fatty acids of the ω3 family from muscle tissue, but in both sexes specific retention of docosahexaenoic acid (DHA=22: 6ω3) in muscle is evident. Landlocked shad, unlike several freshwater fishes, can utilize the liver as well as body cavity and muscle as a fat reserve depot. The perivisceral fat stored during the feeding period appears to be utilized mainly for winter energy maintenance requirements. Lipid reserves from liver and muscle are also mobilized to meet the requirements resulting from gonadal development. In particular, females seem to use liver reserves, especially 18: 1ω9, more than males, to meet the demands of ovogenesis. In the muscle, SFA are used mainly for energy purposes. During gonadal development, specific muscular and hepatic ω3 highly unsaturated fatty acids (ω3 HUFA=20: 5 + 22: 5 + 22: 6) and ω6 HUFA (20: 4+22: 4+22: 5) retention is evident in both sexes, while fatty acid precursors of ω3 and ω6 HUFA are mobilized, especially from muscle tissue.     

Interaction of landscape and life history attributes on genetic diversity,neutral divergence and gene flow in a pristine community of salmonids

Landscape genetics holds promise for the forecasting of spatial patterns of genetic diversity based on key environmental features. Yet, the degree to which inferences based on single species can be extended to whole communities is not fully understood. We used a pristine and spatially structured community of three landlocked salmonids (Salvelinus fontinalis, Salmo salar, and Salvelinus alpinus) from Gros Morne National Park (Newfoundland, Canada) to test several predictions on the interacting effects of landscape and life history variation on genetic diversity, neutral divergence, and gene flow (m, migration rate). Landscape factors consistently influenced multispecies genetic patterns: (i) waterfalls created strong dichotomies in genetic diversity and divergence between populations above and below them in all three salmonids; (ii) contemporary m decreased with waterway distance in all three species, while neutral genetic divergence (θ) increased with waterway distance, albeit in only two taxa; (iii) river flow generally produced downstream‐biased m between populations when waterfalls separated these, but not otherwise. In contrast, we expected differential life history to result in a hierarchy of neutral divergence (S. salar > S. fontinalis > S. alpinus) based on disparities in dispersal abilities and population size from previous mark‐recapture studies. Such hierarchy additionally matched varying degrees of spatial genetic structure among species revealed through individual‐based analyses. We conclude that, whereas key landscape attributes hold power to predict multispecies genetic patterns in equivalent communities, they are likely to interact with species‐specific life history attributes such as dispersal, demography, and ecology, which will in turn affect holistic conservation strategies.