Maternal nesting behaviour in city dragons: a species with temperature-dependent sex determination

Abstract

Urban environments present some of the greatest challenges to species survival. This is particularly true for species that exhibit thermally sensitive traits, such as temperature-dependent sex determination (TSD). This is because urban environments not only present species with entirely novel ecosystems, but species will also experience increased temperatures. These temperature increases may result not only in offspring mortality, but also skewed population sex ratios. To persist in cities, urban dwellers with TSD will therefore need to adjust the temperature of the nesting environment, either through phenotypic plasticity or rapid evolution through natural selection. Here, we investigate the nesting ecology of a long-lived, urban dwelling reptile, the eastern water dragon (Intellagama lesueurii), to understand how a TSD species may respond to urban environments. Based on data collected from 72 nests over 2 nesting seasons, we show that city dragons not only dug significantly deeper nests than previously observed across their natural riparian habitat, but also nested in novel substrates. Furthermore, we observed a behaviour not previously described in this species, where mothers travel outside of their core home range to nest. This excursion behaviour potentially represents a greater maternal investment and is linked to the selection of specific microhabitats.

Fitness benefits of male dominance behaviours depend on the degree of individual inbreeding in a polyandrous lizard

“…Mating tactics can be plastic [38]; however, our field observations suggest that switching tactics is uncommon under natural conditions, particularly from dominant to subordinate because dominant males that are defeated are likely to die. Females generally lay twice a year, with clutch sizes averaging around eight eggs [39,47,48]. Survival rates remain to be quantified in the field; however, our field observations indicate that survivorship from hatchling to adult is low, with survival rates increasing after sexual maturity is attained, resulting in low population turnover.…”

“…Parentage assignments were validated in two ways. First, known maternities from field observations of nesting events were compared with Sequoia assignments (see [48]), which matched in all instances. Second, we calculated genetic relatedness using the maximum-likelihood dyadic relatedness estimator [62] in Coancestry [63] and plotted parentage assignments against genetic relatedness (electronic supplementary material, figure S1).…”

Adaptive significance of affiliative behaviour differs between sexes in a wild reptile population

“…Parentage assignments obtained from Sequoia were validated in two ways. First, we compared them to known maternities resulting from field observations of nesting events [ 36 ]. Second, genetic relatedness was calculated using the maximum-likelihood dyadic relatedness estimator [ 37 ] in Coancestry [ 38 ].…”

Can nesting behaviour allow reptiles to adapt to climate change?

“…Analogously, the low-elevation water dragon constructed deeper nests than did their high-elevation counterparts [42]. Australian water dragons dug deeper nests in urban areas than in natural riparian habitats [84].…”