“Extreme climate-induced life-history plasticity in an amphibian”
Francois S. Becker, Krystal A. Tolley, G. John Measey, and Res Altwegg (Feb 2018)
Rainfall determines key life history decisions in a frog
Live for the day—or maybe longer depending on the weather! Researchers discover frogs whose lifespan depends on rainfall
Blue whales live for more than 100 years, while adult mayflies may come and go in a day. Our own lifespan has increased by nearly 10 years over the past generation. We are used to a world where the life expectancy of animals is expected to vary by a few years, but what if your lifespan was linked to the weather? Researchers from University of Cape Town, South African National Biodiversity Institute, and Stellenbosch University have discovered a frog whose likelihood of survival appears to be linked to the amount of winter rainfall in South Africa’s biodiverse fynbos biome.
Rose’s mountain toadlet comes out every winter to breed, but the amount of time the males spend waiting in puddles for females to arrive influences life-expectancy of these tiny toadlets. At only 20-30 mm long, these voiceless toadlets are easily overlooked, but the researchers, Francois Becker, John Measey, Krystal Tolley, and Res Altwegg, undertook a mark-recapture study over 7 years, to reach the finding that whether toadlets live long (4+ years), or just one year, depends on the weather. Surprisingly, ‘good weather’ for frogs (wet winters) was found to reduce survival as animals are thought to spend more time out in the open, while ‘bad weather’ (drier winters) means they abandon the breeding site quicker, resulting in these toadlets living to try again another winter.
The correlation between survival and winter rainfall is truly remarkable, but the exact mechanism determining survival needs more work, and time is running out. The latest IUCN assessment is that this species is Critically Endangered and with climate in the area changing, it could be that changes in the winter rainfall regime could add to existing threats for this special species.
While this is the first known example of a vertebrate with extreme changes survival that appear to be weather dependent, it may simply be due to a lack of sufficient research on the world’s smaller animal species. The researchers suggest that this kind of weather induced longevity change may be far more common than we are aware of, prompting more concern about how changes to the climate may affect wildlife.
Age specific survival and reproduction are closely linked to fitness and therefore subject to strong selection that typically limits their variability within species. Furthermore, adult survival rate in vertebrate populations is typically less variable over time than other life history traits, such as fecundity or recruitment. Hence, adult survival is often conserved within a population over time, compared to the variation in survival found across taxa. In stark contrast to this general pattern, we report evidence of extreme short-term variation of adult survival in Rose’s Mountain Toadlet (Capensibufo rosei), which is apparently climate-induced. Over seven years, annual survival rate varied between 0.04 and 0.92, and 94% of this variation was explained by variation in breeding-season rainfall. Preliminary results suggest that this variation reflects adaptive life-history plasticity to a degree thus far unrecorded for any vertebrate, rather than direct rainfall induced mortality. In wet years, these toads appeared to achieve increased reproduction at the expense of their own survival whereas in dry years, their survival increased at the expense of reproduction. Such environmentally induced plasticity may reflect a diversity of life-history strategies not previously appreciated among vertebrates.