Life history influences how fire affects genetic diversity in two lizard species

Abstract

25 26 'Fire mosaics' are often maintained in landscapes to promote successional diversity in 27 vegetation with little understanding of how this will affect ecological processes in animal 28 populations such as dispersal, social organisation and re-establishment. To investigate these 29 processes, we conducted a replicated, spatio-temporal landscape genetics study of two 30Australian woodland lizard species (Amphibolurus norrisi (Agamidae) and Ctenotus atlas 31 (Scincidae)). Agamids have a more complex social and territory structure than skinks, so fire 32 might have a greater impact on their population structure and thus genetic diversity. Genetic 33 diversity increased with time since fire in C. atlas and decreased with time since fire in A. 34norrisi. For C. atlas, this might reflect its increasing population size after fire, but we could not 35 detect increased gene flow that would reduce loss of genetic diversity through genetic drift. 36Using landscape resistance analyses, we found no evidence that post-fire habitat succession or 37 topography affected gene flow in either species and we were unable to distinguish between 38 survival and immigration as modes of post-fire re-establishment. In A. norrisi, we detected 39 female-biased dispersal, likely reflecting its territorial social structure and polygynous mating 40 system. The increased genetic diversity in A. norrisi in recently burnt habitat might reflect a 41 temporary disruption of its territoriality and increased male dispersal, a hypothesis that was 42 supported with a simulation experiment. Our results suggest that the effects of disturbance on 43 genetic diversity will be stronger for species with territorial social organisation. 44 45

Dispersal responses override density effects on genetic diversity during post-disturbance succession

“…Nephrurus stellatus is a disturbance specialist and was an exemplar for testing our hypothesis about the effects of habitat succession [58]. Genetic diversity can increase with succession in species which rely on late successional vegetation [7,22] meaning that early successional vegetation might impose a dispersal barrier to late successional species. Future work should quantify disturbance effects on dispersal in a range of taxa with different responses to disturbance.…”

“…Regression of distance matrices also indicated significant effects of the TSF-linear and fire frequency models (electronic supplementary material, table S5). Fire frequency and TSF are correlated in this landscape [22] so it is not clear which variable is the key driver of gene flow patterns. However, both of these results indicate that fire increases gene flow in N. stellatus and that gene flow declines in unburnt habitat.…”

“…Sample size (N) varied across sites so we standardized allelic richness, H O and H E to N ¼ 5 to encompass the full site variation in time since fire (TSF). We conducted a sensitivity analysis to test whether sample size (N ¼ 6 -10) influenced effects of TSF on site-level genetic diversity [22]. As N increased, the number of sites included in the analysis decreased, so we lost power to test effects of TSF, but were able to determine whether the general patterns were consistent.…”

“…individual rather than population-based analyses). Where small sample sizes were unavoidably used in our analyses, we challenged our results with sensitivity analysis to ensure that changing sample sizes did not affect our overall conclusions [22]. The link between data and simulation is the strongest aspect of our study.…”

“…We used linear mixed-effects models in the R [29] package 'lme4' [30] to examine if TSF affected allelic richness, H O and H E for each N [22]. Multiple sites were sampled within a single fire boundary, so we fitted fire (a factor naming individual fire events) as a random effect.…”