Do life history strategies explain differential population structure of three desert amphibians?

Background/Question/Methods

Dryland streams play a prominent role in shaping hydrological, biogeochemical, and ecological structure of arid and semi-arid ecosystems. Many amphibians of the Madrean Sky Islands of the Sonoran Desert rely on streamflows generated by winter storms and summer monsoons that provide favorable breeding habitat and hydrologic connectivity with individuals or populations that are otherwise isolated by harsh and dry habitat. The predictability, frequency, and magnitude of these flows will likely be altered by climate change and increasing human requirements for freshwater. Examining population structure of desert amphibians - and its relationship to hydrology - is an important step in understanding how these species may be affected by these stressors. We present results of a landscape genetic analysis of three desert amphibians common to the Madrean Archipelago: Spea multiplicata (Mexican spadefoot), Anaxyrus punctatus (red-spotted toad), and Hyla arenicolor (canyon treefrog). Although all three species are well-adapted for life in an arid landscape, they span a range of life history strategies enabling them to survive in a region where water is often scarce. Using a landscape genetics approach (microsatellite markers), we examine the extent to which life history variation and hydrologic dependence predict the role of various landscape variables in structuring the population genetics of these species. 

Results/Conclusions

Individuals of all three target species were collected during the spring and summer of 2010, 2011, and 2012 from the Huachuca, Santa Rita, Mule, Whetstone, and Dragoon Mountain ranges in Southeast Arizona (average putative populations per species = 21; average individuals per population = 30; average markers per species = 14).  Preliminary results show that the degree and nature of the relationships between genetic connectivity and landscape variables (e.g., slope and major riparian networks) vary by species and life history. Our results also highlight a positive relationship between increasing population differentiation and hydrologic dependence, e.g. longer larval development periods and site fidelity for reliable water sources like bed rock pools. Ultimately, managing for freshwater ecosystem integrity – and conservation of aquatic species – requires basic knowledge of population structure and connectivity. By providing a baseline assessment of population structure of three common desert amphibians, we aim to provide fundamental information critical to native amphibian conservation efforts and planning in the American Southwest in the face of climate change and increasing human freshwater use.