Impact of climate change on the physiology and distribution of <em>Eleutherodactylus portoricensis</em>

Abstract

Global climate is changing at unprecedented rates, causing detrimental effects on vulnerable organisms and forcing them to cope with unfavorable conditions. Ectotherms often adapt to changing abiotic variables by altering their distribution ranges. Amphibians are known to alter their distribution because of rising temperatures. In Puerto Rico we have observed a range-shift to higher elevations in one species of direct-developing frog. Here we considered two species that occur sympatrically in part of their range at El Yunque tropical montane reserve. One species, <em>Eleutherodactylus portoricensis</em>, is presently limited to high elevations above 700 m.a.s.l., although it was previously found down to 400 m.a.s.l. Contrastingly, its congeneric <em>E. coqui</em>, can be found at all elevations (0-1,300 m.a.s.l.). Our objective was to characterize both species&rsquo; thermo-physiological profiles and question if the observed range-shift to higher elevations of <em>E. portoricensis</em> was associated to higher physiological sensitivity. We evaluated critical thermal minima and maxima, and thermal preference for three populations: <em>E. portoricensis</em> (850m), and low (180m) and highland (850m) <em>E. coqui</em>. We also evaluated dehydration stress during jumping performance by reducing 5% of their body mass using dry-air chambers. Lastly, we modeled <em>E. portoricensis</em> current and future distribution range under various scenarios of climate change. Our results show that <em>E. portoricensis</em> has a narrower thermal tolerance range and prefers lower temperatures when given a gradient. Also, <em>E. portoricensis</em> showed lower performance levels than <em>E. coqui</em> when dehydrated. Our results suggest that higher physiological sensitivity may explain elevational range contraction on this species. In addition, distribution models show a decrease in occurrence probability later this century in comparison to current projections. Our models also predict a range contraction towards higher elevations. This range shift would most likely result in the extirpation of most <em>E. portoricensis</em> populations. This research highlights the vulnerability of an endemic tree frog in Puerto Rico as a consequence of anthropogenic climate change and the urge to develop effective conservation efforts.