Abstract
Infectious diseases can alter the demography of their host populations, reducing their viability even in the absence of mass mortality. Amphibians are the most threatened group of vertebrates globally, and emerging infectious diseases play a large role in their continued population declines. Viruses belonging to the genus Ranavirus are responsible for one of the deadliest and most widespread of these diseases. To date, no work has used individual level data to investigate how ranaviruses affect population demographic structure. We used skeletochronology and morphology to evaluate the impact of ranaviruses on the age structure of populations of the European common frog (Rana temporaria) in the UK. We compared ecologically similar populations that differed most notably in their historical presence or absence of ranavirosis (the acute syndrome caused by ranavirus infection). Our results suggest that ranavirosis may truncate the age structure of R. temporaria populations. One potential explanation for such a shift might be increased adult mortality and subsequent shifts in the life history of younger age classes that increase reproductive output earlier in life. Additionally, we constructed population projection models which indicated that such increased adult mortality could heighten the vulnerability of frog populations to stochastic environmental challenges.
Highlights
The emergence of infectious diseases can truncate the age structure of host populations (Jones et al, 2008; Lachish, McCallum & Jones, 2009; Ohlberger et al, 2011; Fitzpatrick et al, 2014)
We found that older R. temporaria are significantly less likely to be found within populations with a positive history of ranavirosis than they are in disease-free populations
Our results highlight an increasing need to better understand the impact of disease on the demography of host populations and the processes which can bring about such demographic shifts
Summary
The emergence of infectious diseases can truncate the age structure of host populations (Jones et al, 2008; Lachish, McCallum & Jones, 2009; Ohlberger et al, 2011; Fitzpatrick et al, 2014). To maximise individual fitness within an environment of high extrinsic adult mortality, selection for increased developmental rates, decreased size, and age at sexual maturity, and an increased adult life span (decreased intrinsic adult mortality) will occur (Stearns et al, 2000). This theory has been empirically borne out in a number of systems in response to several different sources of mortality, including predation (Reznick, Bryga & Endler, 1990), over-harvesting (Olsen et al, 2004), and experimentally induced adult mortality (Stearns et al, 2000)
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