The canonical model of sex-chromosome evolution predicts that, as recombination is suppressed along sex chromosomes, gametologs will progressively differentiate, eventually becoming heteromorphic. However, there are numerous examples of homomorphic sex chromosomes across the tree of life. This homomorphy has been suggested to result from frequent sex-chromosome turnovers, yet we know little about which forces drive them. Here, we describe an extremely fast rate of turnover among 28 species of Ranidae. Transitions are not random, but converge on several chromosomes, potentially due to genes they harbour. Transitions also preserve the ancestral pattern of male heterogamety, in line with the ‘hot-potato’ model of sex-chromosome transitions, suggesting a key role for mutation-load accumulation in non-recombining genomic regions. The importance of mutation-load selection in frogs might result from the extreme heterochiasmy they exhibit, making frog sex chromosomes differentiate immediately from emergence and across their entire length.

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Accurate trend estimates are necessary for understanding which species are declining and which are most in need of conservation action. Imperfect species detection may result in unreliable trend estimates because this may lead to the overestimation of declines. Because many management decisions are based on population trend estimates, such biases could have severe consequences for conservation policy. We used an occupancy-modeling framework to estimate detectability and calculate nationwide population trends for 14 Swiss amphibian species both accounting for and ignoring imperfect detection. Through the application of International Union for Conservation of Nature Red List criteria to the different trend estimates, we assessed whether ignoring imperfect detection could affect conservation policy. Imperfect detection occurred for all species and detection varied substantially among species, which led to the overestimation of population declines when detectability was ignored. Consequently, accounting for imperfect detection lowered the red-list risk category for 5 of the 14 species assessed. We demonstrate that failing to consider species detectability can have serious consequences for species management and that occupancy modeling provides a flexible framework to account for observation bias and improve assessments of conservation status. A problem inherent to most historical records is that they contain presence-only data from which only relative declines can be estimated. A move toward the routine recording of nonobservation and absence data is essential if conservation practitioners are to move beyond this toward accurate population trend estimation. AbstractAccurate trend estimates are necessary for understanding which species are declining and which are most in need of conservation action. Imperfect species detection may result in unreliable trend estimates because this may lead to the overestimation of declines.As many management decisions are based on population trend estimates, such biases could have severe consequences for conservation policy. We used an occupancy modelling framework to estimate detectability and calculate nationwide population trends for 14 Swiss amphibian species both accounting for and ignoring imperfect detection. Through application of IUCN Red List criteria to the different trend estimates, we assessed whether ignoring imperfect detection could impact on conservation policy. Imperfect detection was seen in all species and detection varied substantially among species, which led to the overestimation of population declines when detectability was ignored. Consequently, accounting for imperfect detection lowered the red-list risk category for 5 of the 14 species assessed. We demonstrate that failing to consider species detectability can have serious consequences for species management, and that occupancy modelling provides a flexible framework to account for observation bias and improve assessments of conservation status. A problem inherent to most historical records is tha...

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Rapid management responses against invasive species soon after their establishment are the most efficient way to limit their biological and economic impacts. Early detection and reliable monitoring is however challenging when cryptic taxa are involved. Here we show how environmental DNA (eDNA) metabarcoding of water samples efficiently unveiled an emerging invasion of Italian crested newts (Triturus carnifex), one of the most successful amphibian invaders in Europe. We compared and validated an eDNA survey by multilocus population genetics of wild-caught individuals. Both approaches consistently mapped a localized T. carnifex invasion in northwestern Switzerland, most likely following imports from the Italian Po Plain. We found evidence of gene flow with the indigenous and endangered Triturus cristatus in nearby populations, suggesting a potential expansion. Yet the currently small invasive range should be efficiently contained by future eradication programs. This textbook case emphasizes the implementation of eDNA metabarcoding to screen aquatic communities for exotic species, from which targeted studies can be designed on emerging biological invasions.