Complex Organisms Must Deal with Complex Threats: How Does Amphibian Conservation Deal with Biphasic Life Cycles?

Abstract

The unprecedented rate of global amphibian decline is attributed to The Anthropocene, with human actions triggering the Sixth Mass Extinction Event. Amphibians have suffered some of the most extreme declines, and their lack of response to conservation actions may reflect challenges faced by taxa that exhibit biphasic life histories. There is an urgent need to ensure that conservation measures are cost-effective and yield positive outcomes. Many conservation actions have failed to meet their intended goals of bolstering populations to ensure the persistence of species into the future. We suggest that past conservation efforts have not considered how different threats influence multiple life stages of amphibians, potentially leading to suboptimal outcomes for their conservation. Our review highlights the multitude of threats amphibians face at each life stage and the conservation actions used to mitigate these threats. We also draw attention to the paucity of studies that have employed multiple actions across more than one life stage. Conservation programs for biphasic amphibians, and the research that guides them, lack a multi-pronged approach to deal with multiple threats across the lifecycle. Conservation management programs must recognise the changing threat landscape for biphasic amphibians to reduce their notoriety as the most threatened vertebrate taxa globally.

The Increasing Role of Short-Term Sperm Storage and Cryopreservation in Conserving Threatened Amphibian Species

“…Considering the complexity of the multiple threats to biodiversity that amphibians are facing, including the potential for synergistic effects, in situ conservation efforts alone are often insufficient for species recovery [4]. Subsequently, conservation practitioners are being encouraged to adopt integrated, multifaceted approaches to amphibian conservation, including the application of both ex situ and in situ strategies [10][11][12]. Reproductive technologies (RTs, also known as assisted reproductive technologies (ARTs)) offer a suite of tools to improve the propagation and genetic management of threatened species, including technologies to reinvigorate genetic diversity and facilitate genetic exchange between living captive and wild populations, as well as from expired generations [10,13,14].…”

Framework for multi-stressor physiological response evaluation in amphibian risk assessment and conservation

“…Effective adaptive conservation management strategies target vulnerable life stages and critical threats to wildlife populations. The biphasic life cycle of anuran amphibians makes them particularly vulnerable to extrinsic stressors because of their dependence on variable aquatic habitat resources as well as terrestrial environmental quality (Nolan et al, 2023). Their complex life history strategy and multiple potential drivers of population decline require a more nuanced approach to targeting spatial and temporal variability in stressors relative to life stage (Walls and Gabor, 2019;Awkerman et al, 2020).…”

“…Their complex life history strategy and multiple potential drivers of population decline require a more nuanced approach to targeting spatial and temporal variability in stressors relative to life stage (Walls and Gabor, 2019;Awkerman et al, 2020). Distinguishing stagespecific endogenous variation in physiological processes enables anticipation of compromised physical condition in response to common stressors (Brooks and Kindsvater, 2022;Nolan et al, 2023). Here we focus on stressor impacts on transition between life (Denver, 2009;Duarte-Guterman et al, 2014;Thambirajah et al, 2019) GC ↑ to some xenobiotics (Burraco and Gomez-Mestre, 2016;Trudeau et al, 2020), environmental conditions (Sachs and Buchholz, 2019;Thambirajah et al, 2019), predators (Narayan et al, 2013) ; neurogenerative, oxidative, mitochondrial, teratological effects (Di Lorenzo et al, 2020) CS and TH levels in tissue or immersed water (Gabor et al, 2013a); tissue/ organism enzyme activity or DGE in AR, TR, tra, trb, dio2, dio3 (Thambirajah et al, 2022); ambient water assay; size at metamorphosis (Rowland et al, 2023); vitellogenin indicative of feminization (Venturino and de D'Angelo, 2005) Time to metamorphosis; cohort sex ratio; carryover to juvenile immunity, survival, fecundity (Kiesecker, 2002, Denver, 2009Kohli et al, 2019;Ruthsatz et al, 2020;Le Sage et al, 2022) Immunity Endocrine-driven development of immunity; immunosuppression at metamorphosis (Rollins-Smith, 2017)…”

“…During metamorphic climax, metabolic activity changes, reflecting increasing energy needs, anabolic requirements, and tail apoptosis; these energetic requirements and fasting effects create a vulnerable transition from larva to juvenile in which contaminant body burdens can amplify (Rowland et al, 2023). The aquatic phase of the amphibian life cycle is also susceptible to reduced growth in response to pathogens that have been introduced to waterbodies, although survival is rarely impacted at this stage (Nolan et al, 2023). Although phylogeny and abiotic environmental variables determine the initial likelihood of Bd or ranavirus occurrence in areas of viral compatibility, other stressors such as pesticides can further influence viral loads and the resistance of the host population as well as the prevalence of parasite-induced deformities (e.g., Kerby et al, 2011;Kiesecker, 2011;Pochini and Hoverman, 2017).…”

On the fence: reevaluating the use of temporary amphibian exclusion fencing

“…The Importance of Species-Specific Traits and Site Context Amphibians generally possess a biphasic life history, with projects needing to account for transitions in habitat use between life stages (Dodd 2010;Nolan et al 2023). Fencing impacts will be dependent on the timing of works in relation to a species' life history events (e.g.…”