Effects of learning and adaptation on population viability

Abstract

Cultural adaptation is one means by which conservationists may help populations adapt to threats. A learned behavior may protect an individual from a threat, and the behavior can be transmitted horizontally (within generations) and vertically (between generations), rapidly conferring population-level protection. Although possible in theory, it remains unclear whether such manipulations work in a conservation setting; what conditions are required for them to work; and how they might affect the evolutionary process. We examined models in which a population can adapt through both genetic and cultural mechanisms. Our work was motivated by the invasion of highly toxic cane toads (Rhinella marina) across northern Australia and the resultant declines of endangered northern quolls (Dasyurus hallucatus), which attack and are fatally poisoned by the toxic toads. We examined whether a novel management strategy in which wild quolls are trained to avoid toads can reduce extinction probability. We used a simulation model tailored to quoll life history. Within simulations, individuals were trained and a continuous evolving trait determined innate tendency to attack toads. We applied this model in a population viability setting. The strategy reduced extinction probability only when heritability of innate aversion was low (<20%) and when trained mothers trained >70% of their young to avoid toads. When these conditions were met, genetic adaptation was slower, but rapid cultural adaptation kept the population extant while genetic adaptation was completed. To gain insight into the evolutionary dynamics (in which we saw a transitory peak in cultural adaptation over time), we also developed a simple analytical model of evolutionary dynamics. This model showed that the strength of natural selection declined as the cultural transmission rate increased and that adaptation proceeded only when the rate of cultural transmission was below a critical value determined by the relative levels of protection conferred by genetic versus cultural mechanisms. Together, our models showed that cultural adaptation can play a powerful role in preventing extinction, but that rates of cultural transmission need to be high for this to occur.

A brief history of the northern quoll (

“…The efficacy of CTA as a management strategy is largely dependent on a single factor: whether quolls can confer the learnt toad-aversion lesson between generations via trained mothers teaching their young (cultural transmission). Recently, population viability models demonstrated that the efficacy of CTA as a conservation strategy for northern quolls requires cultural transmission rates (mother training young) of .70% to prevent local extinction (Indigo et al 2021). Unfortunately, there is currently no evidence that quolls have the ability or tendency to train their young to avoid cane toads (Indigo et al 2021).…”

“…Recently, population viability models demonstrated that the efficacy of CTA as a conservation strategy for northern quolls requires cultural transmission rates (mother training young) of .70% to prevent local extinction (Indigo et al 2021). Unfortunately, there is currently no evidence that quolls have the ability or tendency to train their young to avoid cane toads (Indigo et al 2021). Therefore, the transmission of behavioural aversion of cane toads in toad-averse quoll populations (e.g.…”

Novel habitat associations and seasonality in threatened Mitchell’s water monitors (Varanus mitchelli): Implications for conservation

“…2014; Kelly & Phillips 2017; Indigo et al . 2021), with probability of persistence potentially mediated by resource availability (Moore et al . 2019).…”

“…In some cases, populations may persist if individuals possess innate and heritable toad-averse traits that provide them with some resilience to cane toad impacts (e.g. Phillips & Shine 2006;Llewelyn et al 2014;Kelly & Phillips 2017;Indigo et al 2021), with probability of persistence potentially mediated by resource availability (Moore et al 2019). In others, features of the landscape may offer some protection by being less habitable for toads, lessening the impact on vulnerable natives.…”

Population genomics of a predatory mammal reveals patterns of decline and impacts of exposure to toxic toads

“…Because the spread of cane toads has so far proved impossible to halt, current management actions are aimed at mitigating the impact of toads. For example, the Northern Territory government established insurance populations on two offshore islands in 2003 (Rankmore et al, 2008 ), and there is ongoing research into the feasibility of increasing the frequency of toad‐avoidance traits in populations via training (Indigo et al, 2021 ; Jolly et al, 2020 ) or translocation of heritable “toad‐smart” genotypes into toad‐naïve populations (“targeted gene flow”) (Kelly et al, 2021 ; Kelly & Phillips, 2019 ). Critically, these management strategies require understanding and managing various genetic aspects for them to be successfully implemented.…”