Implications of climate change on genetic connectivity of isolated populations

Background/Question/Methods

One likely impact of climate change is the alteration of hydrologic regimes, which will affect many obligatory aquatic species.  Streams in arid regions are particularly sensitive to increases in temperature and altered precipitation patterns.  Aquatic organisms in these arid ecosystems are restricted to fragmented habitats.  Projected increases in temperature and decreases in rainfall have the potential to further reduce habitat availability. Increased isolation caused by climate change may reduce the likelihood of interaction among populations and the chance of successful recolonization after local extinctions, thus threatening metapopulation persistence.  Understanding the consequences of climate change on genetic connectivity and population stability within species distributed across a landscape is important to prioritize management efforts. We have collected three species of aquatic invertebrates with diverse life-history strategies and dispersal abilities (a diving beetle, Stictotarsus aequinoctialis (Dytiscidae), a stonefly, Mesocapnia arizonensis (Capniidae), a water bug, Abedus herberti (Belostomatidae)) from multiple watersheds in ten mountain ranges in the Madrean Sky Island Archipelago in southern Arizona and developed polymorphic microsatellite loci for each.  These data are being used to determine the extent that habitat availability impacts genetic structure across a naturally fragmented habitat; and how changes in population structure impact landscape-level genetic diversity and population stability.

Results/Conclusions

Analysis of microsatellite loci of S. aequinoctialis (over 1000 individuals from 27 populations) shows little sign of population structure.  These results reflect dispersal ability of this species, which is a habitat generalist and a strong flier for much of its life.  M. arizonensis, a species restricted to intermittent stream reaches and with a brief winged adult stage, exhibits a significant isolation-by-distance pattern (over 1000 individuals from 27 populations).  A. herberti, which is flightless and restricted to permanent freshwater habitats, exhibit significant genetic structure, and evidence of migration events being rare (over 800 individuals from 30 populations).  By using multiple taxa with variable life history strategies and dispersal abilities, we can extrapolate these results to similar species, predicting which species are likely to be most negatively impacted by changes to hydrologic regimes.  We aim to use these data to predict thresholds of population size or population connectivity/gene flow, beyond which populations shift from stable to unstable.