Debra M. Shier

Understanding the strength and direction of negative species interactions is essential for managing co‐occurring at‐risk species. The sympatric kangaroo rats Dipodomys stephensi and Dipodomys simulans are both threatened by habitat loss, but conservation efforts have focused on D. stephensi . A fine‐scale habitat partitioning study provided evidence for intense interference competition between the species. To determine whether one species dominates the other, we staged dyadic encounters between residents and intruders in the field. We found a consistent asymmetry: D. simulans avoided D. stephensi , and D. stephensi residents and intruders had a 92% and 76% chance of defeating D. simulans , respectively. These findings suggest that conservation translocations of D. stephensi are unlikely to be negatively affected by D. simulans but could exacerbate ongoing declines in D. simulans , highlighting the need to incorporate behavioral interference into conservation planning and management.

A challenge for conservation breeding and reintroduction programs is low post-release survival due to deficits in critical behavioral competencies in captive-bred animals, such as predator recognition and avoidance. Although antipredator training, in which predator cues are paired with aversive stimuli, can improve behavioral responses, it is often labor-intensive and difficult to scale across captive populations. Maternal effects offer a potential alternative, whereby a mother’s experience influences offspring phenotype. Here, we evaluated whether maternal exposure to predator training during gestation was associated with differences in offspring antipredator behavior and post-release survival in the endangered Pacific pocket mouse ( Perognathus longimembris pacificus ). Pregnant females were exposed to a live snake paired with an aversive stimulus or a control object. Offspring were later assessed during standardized antipredator trials and monitored following release. Maternal predator training during gestation was associated with increased antipredator behaviors in female offspring, but not males. However, these behavioral differences did not correspond to improved post-release survival. Because predator exposure was paired with an aversive stimulus and offspring subsequently underwent standardized training, we cannot isolate prenatal programming from postnatal maternal effects or experience-dependent learning. These findings suggest that maternal experience may influence offspring behavior, but additional work is needed to determine the mechanisms involved and the extent to which such behavioral changes translated to fitness benefits in the wild.

Global climate change poses a substantial challenge for many species, particularly when habitat loss and fragmentation prevent a species from shifting its range to track suitable climate conditions. Instead, these species must adapt in situ to a different climate environment, making their capacity for adaptation critical to persistence. Yet endangered species often face the added challenge of low standing genetic variation needed for an evolutionary response. Here, we assess adaptive potential in the endangered Pacific pocket mouse ( Perognathus longimembris pacificus ). Using whole-genome sequences spanning nearly a century, we identify 14 candidate genes associated with temperature and moisture, including many with vascular and circulatory functions. Using a reintroduced population, we find more alleles than expected by chance shifted toward the frequencies predicted for the climate of the reintroduction locality. Despite extreme population declines over the past century, these findings indicate that conservation breeding and reintroduction have retained genetic variation relevant to adaptive potential in the Pacific pocket mouse.

Gut microbiomes can dramatically affect host health and fitness, but can shift rapidly under changing environmental conditions. Understanding the interplay between microbiota, environmental pressures, and host responses is critical for predicting species’ resilience, particularly in populations transitioning from the wild to human care for conservation breeding. Although captivity can profoundly alter microbial communities and host physiology, the dynamics of these transitions across generations remain poorly understood. We evaluated gut microbiota and fitness metrics in the endangered Pacific pocket mouse ( Perognathus longimembris pacificus ) during the establishment of a conservation breeding and reintroduction program, spanning five generations. Microbiome composition shifted gradually, stabilizing into a distinct captivity-associated state after two to three generations. These transitions paralleled changes in host weight and reproductive performance, suggesting coordinated host–microbiome adaptation. In addition, we identified microbial taxa correlated with successful reproduction, highlighting potential microbial markers of fitness. Our findings provide the first characterization of gut microbiota in Pacific pocket mice and demonstrate how captivity shapes host–microbiome systems across generations. More broadly, they underscore the importance of considering microbiome dynamics in conservation management and suggest that microbial responses to environmental change may require multiple generations to reach a new stable state. IMPORTANCE: In human-altered landscapes, animals face numerous threats to their survival, yet little is known about how rapid environmental change affects host–microbiome dynamics across generations. Microbial communities play critical roles in host nutrition, immunity, and overall fitness, and shifts in composition may alter an organism’s ability to adapt. We examined the gut microbiota of the endangered Pacific pocket mouse during the transition from wild to captive environments and across four descendant generations. We found that the microbiome did not immediately shift with captivity but instead stabilized into a distinct, captivity-associated state only after several generations. This study provides the first characterization of gut microbiota in pocket mice and is the first to show, at this resolution, how a wildlife species’ microbiome adapts to environmental change while tracking health and fitness across generations. Our findings highlight the need to incorporate microbiome dynamics into conservation breeding and management strategies.

La dieta del cacomixtle norteño (Bassariscus astutus) varía estacionalmente y a lo largo de su extensa distribución. Durante el estudio de la subespecie insular y endémica del cacomixtle norteño (B. a. saxicola) en México, una de nuestras cámaras trampa capturó en video a un cacomixtle consumiendo un pez globo (Diodon holocanthus). No se han descrito peces en la dieta de ninguna otra población de la especie. Esta evidencia resulta sorprendente, considerando que los peces globo contienen una potente neurotoxina (tetrodotoxina) en algunos órganos y espinas. Hasta donde tenemos conocimiento, no existe evidencia de resistencia a tetrodotoxina en mamíferos. Se requiere más investigación para determinar si el linaje insular del cacomixtle norteño ha desarrollado resistencia a la toxina, lo que le permitiría aprovechar una nueva fuente de proteína disponible en las islas.

Habitat loss and fragmentation are major drivers of biodiversity decline, reducing connectivity among populations and leading to genetic isolation, loss of diversity, increased inbreeding, and reduced fitness. Translocations that promote gene flow by introducing genetically distinct individuals—a process known as genetic rescue—can mitigate these effects by increasing genetic diversity, alleviating inbreeding, and improving adaptive capacity. However, a limited understanding of a population's demographic history, genetic differentiation, and connectivity can hinder the effective application of genetic rescue. We used the Stephens' kangaroo rat (Dipodomys stephensi), a species threatened by habitat loss and fragmentation in southern California, as a model for developing range‐wide genetic management strategies. We analyzed mitochondrial DNA and microsatellite data to investigate genetic structure and estimate both historical and recent demographic patterns, and we used landscape resistance modeling to assess the impacts of natural and anthropogenic barriers on gene flow. Genetic analyses suggest a relatively recent diversification of Stephens' kangaroo rat populations, with higher allelic diversity concentrated in central populations and reduced diversity in isolated northern and southern populations. Although natural geographic features explain much of the genetic structure, landscape resistance models showed that anthropogenic barriers (e.g., roads, development) play a key role in current genetic isolation and are expected to continue driving population differentiation. To guide management, we used population viability simulations to test translocation strategies aimed at reversing genetic erosion. Repeated translocations were far more effective than single events at boosting heterozygosity and population persistence. The frequency and size of translocations were less important than their continued implementation. For very small populations, concurrent habitat restoration to increase carrying capacity was essential to prevent extirpation. Our findings highlight the value of integrating genetic, demographic, and landscape data into conservation planning. This approach is broadly applicable to other species experiencing habitat fragmentation and population isolation.

Amphibians are among the most threatened vertebrates yet assisted reproductive technologies (ARTs) remain underutilized in their conservation. We developed and evaluated a biologically optimized, non-lethal sperm collection protocol for Rana muscosa , a critically endangered frog in a long-term conservation breeding program. Thirteen hormone treatments were tested across six post-injection time points, and sperm quality was assessed via concentration, motility, osmolality, and pH. Generalized linear mixed models revealed that gonadotropin-releasing hormone (GnRHa) alone significantly outperformed hCG-based regimens. The 3 µg/g GnRHa dose yielded the highest sperm concentration and sustained motility from 3 to 24 hours post-injection. Motility was highest under moderately acidic (pH 6.5–7.0) and hypoosmotic (75–100 mOsm/kg) conditions. To support decision-making, we used a Wildlife Sperm Index (WSI) developed by our team that integrates sperm traits and environmental parameters into a single composite score. While 3 µg/g GnRHa ranked highest by concentration alone, 4 µg/g GnRHa achieved the top WSI score due to greater environmental (pH and osmolality) compatibility. These findings provide the first evidence-based ART protocol for R. muscosa and offer a transferable framework for optimizing gamete collection, IVF, and cryopreservation in line with other amphibian species, advancing both genetic management and species recovery goals.

Two-thirds of Earth’s species have undergone population declines, leaving many vulnerable to genomic erosion and inbreeding depression. Genetic rescue can boost the fitness of small populations, but perceived risks of outbreeding depression can limit its use. We quantified these trade-offs in hundreds of endangered Pacific pocket mice ( Perognathus longimembris pacificus ) by combining whole-genome sequences with fitness data. The impacts of genomic erosion in remnant populations were reversed in an admixed breeding program, suggesting the potential benefits of genetic rescue. However, differences in chromosome numbers increase the risk of genetic incompatibilities. Fitness analyses suggested that although admixed karyotypes may have reduced fertility, non-admixed mice with low heterozygosity and high genetic load had even lower fitness, pointing to a greater risk of extinction if populations remain isolated.