Range‐wide persistence of the endangered arroyo toad (Anaxyrus californicus) for 20+ years following a prolonged drought

Prolonged drought due to climate change has negatively impacted amphibians in southern California, U.S.A. Due to the severity and length of the current drought, agencies and researchers had growing concern for the persistence of the arroyo toad (Anaxyrus californicus), an endangered endemic amphibian in this region. Range‐wide surveys for this species had not been conducted for at least 20 years. In 2017–2020, we conducted collaborative surveys for arroyo toads at historical locations. We surveyed 88 of the 115 total sites having historical records and confirmed that the arroyo toad is currently extant in at least 61 of 88 sites and 20 of 25 historically occupied watersheds. We did not detect toads at almost a third of the surveyed sites but did detect toads at 18 of 19 specific sites delineated in the 1999 Recovery Plan to meet one of four downlisting criteria. Arroyo toads are estimated to live 7–8 years, making populations susceptible to prolonged drought. Drought is estimated to increase in frequency and duration with climate change. Mitigation strategies for drought impacts, invasive aquatic species, altered flow regimes, and other anthropogenic effects could be the most beneficial strategies for toad conservation and may also provide simultaneous benefits to several other native species that share the same habitat.     

Skeletochronological assessment of age structure and population stability for two threatened frog species

Populations that fluctuate in size may become small at particular times and therefore be at risk of extinction. I used skeletochronology to examine the potential for fluctuations in population size in the threatened frog species Geocrinia alba and Geocrinia vitellina from southwestern Australia. The change in number of lines of arrested growth (LAG) in toe bones of recaptured frogs indicated that most individuals probably gain one LAG annually. Therefore, skeletochronology can be used for age determination. From a combination of skeletochronology and a mark–recapture study, both species appear to live for a maximum of six years. However, the majority of adult males only bred in a single year, which gave rise to a consistently dominant three-year-old age class. A drop in the number of two-year-old frogs and a large increase in the number of three-year-olds (up to 85%) from 1993 to 1994 in both species highlighted the potential for substantial fluctuations in population size. Widespread changes in abundance of between 25 and 50% may therefore be expected over periods as short as one or two years, due to variation in recruitment success.     

Mixed population genomics support for the central marginal hypothesis across the invasive range of the cane toad (Rhinella marina) in Australia

Understanding factors that cause species' geographic range limits is a major focus in ecology and evolution. The central marginal hypothesis (CMH) predicts that species cannot adapt to conditions beyond current geographic range edges because genetic diversity decreases from core to edge due to smaller, more isolated edge populations. We employed a population genomics framework using 24 235–33 112 SNP loci to test major predictions of the CMH in the ongoing invasion of the cane toad (Rhinella marina) in Australia. Cane toad tissue samples were collected along broad‐scale, core‐to‐edge transects across their invasive range. Geographic and ecological core areas were identified using GIS and habitat suitability indices from ecological niche modelling. Bayesian clustering analyses revealed three genetic clusters, in the northwest invasion‐front region, northeast precipitation‐limited region and southeast cold temperature‐limited region. Core‐to‐edge patterns of genetic diversity and differentiation were consistent with the CMH in the southeast, but were not supported in the northeast and showed mixed support in the northwest. Results suggest cold temperatures are a likely contributor to southeastern range limits, consistent with CMH predictions. In the northeast and northwest, ecological processes consisting of a steep physiological barrier and ongoing invasion dynamics, respectively, are more likely explanations for population genomic patterns than the CMH.     

The declining Spadefoot toad, Pelobates fuscus (Pelobatidae): paleo and recent environmental changes as a major influence on current population structure and status

Populations of the European Spadefoot toad (Pelobates fuscus) have experienced recent declines all over Europe, but these appear to be more intense in north and western Europe. Due to the toad’s fossorial nature and specific habitat requirements, environmental conditions have played a major role in structuring current populations. We examined the phylogeographic structure in P. fuscus from 16 localities throughout Europe using mitochondrial cytochrome b gene sequence analysis. Sequence divergence among haplotypes was low (0.54±0.15%). Three very closely related haplotypes occupy northern and western parts of Europe whereas 12 others were observed among samples from south-eastern Europe, including the Balkans. Our results suggest that toads only recently colonized the northern and western parts of Europe following glacial retreat. This expansion probably took place in steppic-like areas during the younger Dryas cold interval, about 12,900–11,500 years ago. Restricted gene flow with an isolation-by-distance population structure characterises a major part of its distribution range. Based on our results we suggest that the northern and western lineages should be considered as distinct conservation units, while the south-eastern populations from the refugial areas, where nearly all genetic polymorphism occurs and populations appear less vulnerable, should receive special attention.     

Genetic structure of the threatened Phaedranassa schizantha (Amaryllidaceae)

Phaedranassa schizantha (Amaryllidaceae) is an endangered species endemic to Ecuador and two varieties have been described: P. schizantha var. schizantha and P. schizantha var. ignea. We assessed population genetic structure and demographic patterns in 11 populations across the range of the species using 13 microsatellite loci. Our data show that genetic diversity was generally lower in the southern part of the range and was especially low in populations closest to cities. We found significant population differentiation (F_ST = 0.14, D_EST = 0.34) and evidence of a genetic bottleneck. Genetic variation did not show isolation by distance. Instead, results suggest genetic barriers around two main cities. Bayesian analysis identified two genetic groups, neither of which represents either of the two varieties previously recognized. Coalescent analysis indicates a relatively recent colonization pattern between the two genetic groups (< 3000 generations). Conservation efforts need to be taken to facilitate genetic exchange between the groups, especially between locations that seem to be genetically isolated.     

Microsatellite variation and fine-scale population structure in the wood frog (Rana sylvatica)

We investigated genetic population structure in wood frogs (Rana sylvatica) from a series of Prairie Pothole wetlands in the northern Great Plains. Amphibians are often thought to exist in demographic metapopulations, which require some movement between populations, yet genetic studies have revealed strong subdivision among populations, even at relatively fine scales (several km). Wood frogs are highly philopatric and studies of dispersal suggest that they may exhibit subdivision on a scale of approximately 1-2 km. We used microsatellites to examine population structure among 11 breeding assemblages separated by as little as 50 m up to approximately 5.5 km, plus one population separated from the others by 20 km. We found evidence for differentiation at the largest distances we examined and among a few neighbouring ponds, but most populations were strikingly similar in allele frequencies, suggesting high gene flow among all but the most distant populations. We hypothesize that the few significant differences among neighbouring populations at the finest scale may be a transient effect of extinction-recolonization founder events, driven by periodic drying of wetlands in this hydrologically dynamic landscape.     

Shrinking before our isles: the rapid expression of insular dwarfism in two invasive populations of guttural toad (Sclerophrys gutturalis)

Island ecosystems have traditionally been hailed as natural laboratories for examining phenotypic change, including dramatic shifts in body size. Similarly, biological invasions can drive rapid localized adaptations within modern timeframes. Here, we compare the morphology of two invasive guttural toad (Sclerophrys gutturalis) populations in Mauritius and Réunion with their source population from South Africa. We found that female toads on both islands were significantly smaller than mainland counterparts (33.9% and 25.9% reduction, respectively), as were males in Mauritius (22.4%). We also discovered a significant reduction in the relative hindlimb length of both sexes, on both islands, compared with mainland toads (ranging from 3.4 to 9.0%). If our findings are a result of natural selection, then this would suggest that the dramatic reshaping of an amphibian''s morphology—leading to insular dwarfism—can result in less than 100 years; however, further research is required to elucidate the mechanism driving this change (e.g. heritable adaptation, phenotypic plasticity, or an interaction between them).     

Implications of life history uncertainty when evaluating status in the Northwest Atlantic population of white shark (Carcharodon carcharias)

To effectively protect at‐risk sharks, resource managers and conservation practitioners must have a good understanding of how fisheries removals contribute to changes in abundance and how regulatory restrictions may impact a population trajectory. This means they need to know the number of animals being removed from a population and whether a given number of removals will lead to population increases or declines. For white shark (Carcharodon carcharias), theoretical quantities like the intrinsic rate of population increase or rebound potential (ability to increase in size following decline) are difficult to conceptualize in terms of real‐world abundance changes, which limits our ability to answer practical management questions. To address this shortfall, we designed a simulation model to evaluate how our understanding of longevity and life history variability of white shark affects our understanding of population trends in the Northwest Atlantic. Then, we quantified the magnitude of removals that could have caused historical population declines, compared these to biologically based reference points, and explored the removal scenarios which would result in population increase. Our results suggest that removals on the order of 100s of juveniles per year could have resulted in population‐level declines in excess of 60% during the 1970s and 1980s. Conservation actions implemented since the 1990s would have needed to be nearly 100% effective at preventing fishing mortality in order for the population to double in abundance over the last 30 years. Total removals from all fleets needed to be exceptionally small to keep them below biological reference points for white shark in the Northwest Atlantic. The population's inherent vulnerability to fishing pressure reaffirms the need for restrictive national and international conservation measures, even under a situation of abundance increase.     

Conservation of rare species with island-like distributions: A case study of Lasthenia conjugens (Asteraceae) using population genetic structure and the distribution of rare markers

Californian vernal pools, a patchy, island-like habitat, are endangered as a result of habitat destruction. Conservation of the remaining vernal pool habitat is essential for the persistence of several endangered species. We present the first study examining DNA-level genetic diversity within and among populations of a vernal pool plant species. We investigated genetic variation across eight populations of the US federally endangered vernal pool endemic Lasthenia conjugens (Asteraceae) using intersimple sequence repeat (ISSR) markers. Genetic diversity within the species was high (Nei's gene diversity estimate was 0.37), with moderate differentiation among populations (Bayesian F _ST analog of 0.124). Using an amova analysis, we found that the majority of the genetic variation (84%) was distributed within populations. There is a significant relationship between geographical distance and pairwise genetic differentiation as measured by the Bayesian estimate θ^B. The alternative hypotheses of historic geological processes within the Central Valley and contemporary gene flow are discussed as explanations of the data. Because of the vulnerability of the populations, we calculated a probability of loss for rare alleles (fragments) in the populations. Calculations show that sampling only one of the eight populations for ex-situ conservation or restoration will capture approximately 54% of the sampled rare fragments. We believe that one of the sampled populations has become extinct since it was sampled. When removing this population from the above-mentioned calculations, sampling one population will capture only 41.3% of the sampled rare fragments. We recommend sampling strategies for future conservation and restoration efforts of L. conjugens.     

Microsatellite variation and population structure of the moor frog (Rana arvalis) in Scandinavia

Several recent studies have found amphibian populations to be genetically highly structured over rather short geographical distances, and that the rate of genetically effective dispersal may differ between the sexes. However, apart from the common frog ( Rana temporaria ) little is known about the genetic structuring and sex-biased dispersal in northern European amphibians. We investigated the patterns of genetic diversity and differentiation within and among Scandinavian populations of the moor frog ( Rana arvalis ) using microsatellite markers. The genetic diversity within local R. arvalis populations was not a simple linear negative function of latitude but a convex one: genetic diversity peaked in mid-latitude populations, and declined thereafter dramatically towards the north. The average degree of genetic differentiation among populations ( F _ST = 0.14) was lower than that observed for the common frog ( F _ST = 0.21), though the pattern of isolation by distance was similar for both species. Contrary to common frogs, no evidence for female-biased dispersal was found. The results reinforce the view that amphibian populations are—in general—highly structured over relatively small geographical distances, even in comparatively recently colonized areas.     

Postglacial expansion and not human influence best explains the population structure in the endangered kea (Nestor notabilis)

Inferring past demography is a central question in evolutionary and conservation biology. It is, however, sometimes challenging to infer the processes that shaped the current patterns of genetic variation in endangered species. Population substructuring can occur as a result of survival in several isolated refugia and subsequent recolonization processes or via genetic drift following a population decline. The kea (Nestor notabilis) is an endemic parrot widely distributed in the mountains of the South Island of New Zealand that has gone through a major human‐induced population decline during the 1860s–1970s. The aims of this study were to understand the glacial and postglacial history of kea and to determine whether the recent population decline played a role in the shaping of the current genetic variation. We examined the distribution of genetic variation, differentiation and admixture in kea using 17 microsatellites and the mitochondrial control region. Mitochondrial data showed a shallow phylogeny and a genetic distinction between the North and South of the range consistent with the three genetic clusters identified with microsatellite data. Both marker types indicated an increase in genetic isolation by geographic distance. Approximate Bayesian Computation supported a scenario of postglacial divergence from a single ancestral glacial refugium, suggesting that the contemporary genetic structure has resulted from recolonization processes rather than from a recent population decline. The recent evolutionary origin of this genetic structure suggests that each genetic cluster does not need to be considered as independent conservation units.     

Synaptic mutation associated with gametic sterility and population divergence in Coptis teeta (Ranunculaceae)

Cytogenetic investigations of 13 natural populations of Coptis teeta , an endemic and endangered medicinal plant from the Eastern Himalaya, were carried out. About 70–80% individuals in some of the populations were synaptic mutants. The predominantly sexually breeding plant populations were confined to higher cooler latitudes, whereas the mutant apomict inhabited lower warmer latitudes. The breeding systems were observed to be associated with morphological differentiation and ecological preference of some populations. Individuals of subsp. teeta reproduced sexually as well as vegetatively, but those of subsp. lohitensis have adapted almost entirely to a vegetative mode of reproduction. Though no variation was observed in somatic chromosome number and karyotypes, the two subspecies differed significantly with respect to their male meiotic behaviour and rhizome morphology. The mutants either produced little fertile pollen or were completely sterile, leading to low seed production or none at all. This has resulted in low reproductive fitness, localized distribution and small population sizes of the taxon.     

New distribution data and population structure of the European mudminnow Umbra krameri in Serbia and Bosnia and Herzegovina

Seventy‐six individuals of the European mudminnow Umbra krameri from two recent populations from Serbia (Bakreni Batar and Lugomir) and one from Bosnia and Herzegovina (Gromi?elj) were analysed for habitat preferences and population structure. The population from Lugomir is a newly recorded population in Serbia. Besides this new record, it is noteworthy that all three studied locations are outside the currently known species distribution range limits.     

Genetic structure of the rare and endangered Hieracium wiesbaurianum group (Asteraceae) in Bavaria

The rare and endangered Hieracium wiesbaurianum species group shows a scattered relictual distribution in Bavaria. Recently, a couple of populations were discovered which clearly differ from all other populations. If these must be considered as taxonomically independent units, they would be of crucial conservation interest, because of the sole responsibility that Bavaria has for these worldwide endemics. We therefore analysed the genetic structure of H. wiesbaurianum in a comparative approach. Our analysis comprised 37 populations of 13 taxa of H. wiesbaurianum, H. bifidum and H. laevigatum, including three potentially new taxa. We applied amplified fragment length polymorphism (AFLP) analysis and observed only limited genetic variation within populations and taxa. Nevertheless, each studied individual exhibited a unique genotype. An analysis of molecular variance revealed high levels of genetic variation between taxa, but populations were genetically less different. The clear genetic differentiation between the studied taxa was supported by neighbor‐joining cluster analyses and principal coordinate analyses in which every individual was clearly assigned to its respective taxon. The three potentially new taxa were genetically as well differentiated as the other taxa included in our study. This supports the assumption that they should be treated as taxonomically independent units of high conservation interest. Therefore, the genetic analysis confirmed the morphologically based classification of the studied Hieracium taxa. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 112–123.     

Anthropogenic causes of the western Steller sea lion Eumetopias jubatus population decline and their threat to recovery

• 1 The western Steller sea lion Eumetopias jubatus population has experienced a chronic decline since the 1960s. The causes are likely multifactorial and a combination of anthropogenic and natural factors. A draft revised recovery plan for the Steller sea lion has been published by the US National Marine Fisheries Service, listing both anthropogenic and natural factors that may have contributed to the observed decline or which may be a threat to the recovery of the western Steller sea lion population. The purpose of this review is to consider the anthropogenic threats to this stock.
• 2 Anthropogenic sources of mortality include fisheries competition resulting in nutritional stress, mortality incidental to commercial fisheries (i.e. fisheries by‐catch), subsistence hunts, legal and illegal shooting, commercial hunts, anthropogenic‐related contamination, and research‐induced mortalities.
• 3 We present evidence that the following anthropogenic factors likely contributed to the decline of the western Steller sea lion population over the last 40 years: (i) mortality incidental to commercial fisheries (i.e. by‐catch); (ii) commercial hunting of western Steller sea lions; and (iii) legal and illegal shooting; whereas the subsistence hunts for western Steller sea lions and mortality incidental to research were not likely to be contributors to the observed decline.
• 4 Further, we present evidence that the following can be excluded as significant anthropogenic threats to the recovery of the western Steller sea lion population: (i) mortality incidental to commercial fishing; (ii) legal and illegal shooting; (iii) commercial hunts of Steller sea lions; (iv) subsistence hunting; and (v) mortality incidental to research.
• 5 Competition with fisheries resulting in nutritional stress, and the potential impacts of contaminants, are two anthropogenic factors that should continue to be a priority for the various organizations currently doing research on this population.

     

Genetic relationships and population structure within taxa of the endemic Sideritis pusilla (Lamiaceae) assessed using RAPDs

RAPD analysis has been performed for 15 plant populations, covering eight different infraspecific taxa of Sideritis pusilla (Lange) Pau, member of the Lamiaceae endemic to southeastern Spain, and their putative parental species Sideritis hirsuta L. and Sideritis Uucantha Cav. Genetic distances, together with the presence of numerous fixed molecular markers differentiating S. pusilla from its putative ancestors, indicate that it should be considered as a true species. Cladistic and populational analysis led to the allocation of S. pusilla populations into three major groups– osteoxylla, jlavovirens and pusilla/almeriensis –which include taxa previously described as ranging from the varietal to the specific level. Low genetic differentiation among groups revealed by a reduced number of specific molecular markers justify their assignment under the infraspecific range. Moreover, the existence of both morphological and biogeographical differences, supports a status for these groups as subspecies of S. pusilla. Highly significant ( P <0.002) variance partitioning data (AMOVA) extracted from the analysis of individuals within S. pusilla populations show that, of the total genetic diversity, 68.8% was attributable to individual differences within populations, 19.9% to populational differences within groups, and only 11.3% to divergence between groups. This distribution is in agreement with the outcrossing nature of these plants. Comparative analysis of variance within populations reveals a reduced genetic variation for the osteoxylla group, thus supporting its previous consideration as an endangered taxon.     

Photoperiod manipulation to increase the productivity of black‐footed ferrets (Mustela nigripes) and Siberian polecats (M. eversmanii)

The endangered black‐footed ferret (Mustela nigripes) reproduces naturally in the spring. The Black‐Footed Ferret Recovery Program would benefit from increased productivity in the captive population by manipulating photoperiod and temperature to create three artificial cycles in 1½ years. In the present study the photoperiod was set at 8 hr light:16 hr dark for 1–2 months, then switched to 16 hr light:8 hr dark for 4–5 months. The males' light was switched 1 month before the females' light. Three cycles were performed in 2 years. During the first cycle, 0% of the males bred, 17% of the females came into estrus and were bred through artificial insemination, and 0% of the females whelped. In the second cycle, 100% of the females came into estrus and were bred naturally, and 77% whelped. In the third cycle, all males showed testicular recrudescence but none bred; all females showed signs of estrus, 40% were bred using artificial insemination, and 0% whelped. Siberian polecats (Mustela eversmanii), the black‐footed ferrets' closest living relative, also were put on an artificial photoperiod, coinciding with the black‐footed ferrets' third cycle. All female polecats came into estrus and were bred naturally, and 33% whelped. All males showed testicular recrudescence, and 22% produced sperm and bred. The low rate of success in breeding and whelping suggests that multiple cues may be needed to induce estrus in ferrets and polecats. Zoo Biol 22:1–14, 2003. © 2003 Wiley‐Liss, Inc.     

Biogeography of the smooth snake (Coronella austriaca): origin and conservation of the northernmost population

Understanding historical range expansions and population demography can be crucial for the conservation and management of endangered species. In doing so, valuable information can be obtained regarding, for example, the identification of isolated populations, associations to particular habitats and distribution range shifts. As poikilotherms, snakes are vulnerable to environmental changes that can greatly shape their distribution ranges. Here we used mitochondrial data to elucidate the origin of the smooth snake population in Åland island, which is the northernmost location where the species is found. In Åland, we used mitochondrial and microsatellite data to fine‐map its spatial genetic structure, infer its demographic dynamics and determine its effective population size. We found three independent lineages, which expanded north from Iberian, the Balkans and Caucasus regions. The central lineage originating in the Balkans was the only one that reached Scandinavia. The Åland population belongs to this lineage and potentially colonized the island from the west via Sweden. This population appeared to be critically small and fragmented into two genetically isolated subpopulations. We discuss our results in light of previous findings regarding colonization routes in Europe and Scandinavia. Moreover, we discuss the origin and current genetic status of the Åland population relative to other co‐occurring snakes and suggest conservation measures based on our findings. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 426–435.     

A population genetic study of the endangered plant species Limonium dufourii (Plumbaginaceae) based on amplified fragment length polymorphism (AFLP)

Limonium dufourii ( Plumbaginaceae ) is a triploid species with obligate apomictic reproduction and is endemic to the East Mediterranean coast of Spain, where it is present in only six populations, most of which have a very low number of individuals. Genetic variation and population structure in this species was studied using amplified fragment length polymorphisms (AFLPs) as markers, using the same individuals as in a previous study with random amplified polymorphic DNA (RAPD). Three different primers provided 252 bands of which 51 were polymorphic among the 152 individuals analysed. Those polymorphic bands were able to define 65 different phenotypes, of which all but two were present in only one population. The comparative analyses of data from AFLPs with those from RAPDs show a high degree of concordance. Additionally, and given the nature of these markers, we propose the estimation of nucleotide divergences from AFLP patterns. Relationships among the different AFLP patterns and the estimates of population genetic parameters obtained with this evolutionary distance are in good agreement with previous results. These analyses show that substantial genetic variability and differentiation exist within and among populations of L. dufourii . Their higher reproducibility and the possibility of obtaining estimates of nucleotide divergence make AFLPs a much better DNA fingerprinting technique.     

Alarming decline and range reduction of the highly threatened Great Bustard Otis tarda in Morocco

A Great Bustard Otis tarda survey carried out in spring 2015 in Morocco confirmed the decline of this highly endangered population. Bustards were only seen at two of the seven leks occupied ten years ago. The total number of birds counted was 40-44, which represents a 40% decline over the last decade. The sex-ratio was still strongly female-biased (1 male: 3 females), but less than in previous surveys, which suggests that trophy hunting has not been the major mortality cause in recent times. The productivity was 0.29-0.33 juveniles per female, the highest ever recorded in this population, suggesting that breeding success doesn’t represent the main problem for the survival of this population. Based on the recent development of the power line network at some areas, the main threat today is probably collision with power lines. Reducing this mortality cause should be considered a high conservation priority.