Biology subjects

Hasik, A. Z.

Publications and source records attributed to Hasik, A. Z..

5 recordsLinked to original sources

bioRxiv2026

Patterns of association between mothers and offspring and their outcomes in a polygynous ungulate

Prolonged association between mothers and their offspring is common in ungulates, with the level of maternal investment likely to play a central role in shaping this trait. Here we examined patterns of association between mothers and offspring over time, the apparent benefits of association to offspring, and costs to mothers. We analyzed 40 years worth of census data from an individually-monitored, food-limited population of red deer (Cervus elaphus) on the Isle of Rum, Scotland. Starting from birth, female calves associated more frequently with their mothers than male calves in their first year. Calves also associated less with their mothers if the mother did not conceive a new calf. Association frequency decreased with mothers age and population density, and survival over the first year was not related to mother-calf association. Yearlings, now in their second year, were more often associated with their mothers if they were female, if there was no subsequent calf (or the subsequent calf died as a neonate), and if they were still being suckled. Increased association between mothers and yearlings was associated with increased survival to adulthood at 28 months, but suckling a yearling did not improve its probability of survival. For individuals that reached maturity, increased association in the yearling year was associated with slightly shorter adult life spans. The level of association between a calf and mother was not associated with the mothers immediate survival or fecundity. Our findings suggest that juveniles born to poor-condition mothers benefit from prolonged association through improved yearling survival.

animal behavior and cognition↗

bioRxiv2026

Warmer world gets sicker: meta-analysis reveals strong increase in parasitism at elevated temperatures across diverse host-parasite systems

Climate change is expected to alter infectious disease dynamics worldwide, yet evidence that rising temperatures increase infection (warmer, sicker world hypothesis; WSWH) remains equivocal. We conducted a meta-analysis of 775 effect sizes from 124 experimental studies spanning terrestrial, freshwater, and marine host-parasite systems to test whether warming increases parasitism. Elevated temperatures increased infection, producing moderate positive effects on prevalence and infection intensity in non-phylogenetic models. Temperature effects were significant in terrestrial systems and varied markedly among taxa. Strong responses were observed in nematodes and fungal parasites as well as in plant, invertebrate, and bacterial hosts, whereas vertebrates showed little evidence of consistent increases. Phylogenetically-controlled analyses yielded similar but less precise estimates, indicating that responses are unevenly distributed across the Tree of Life. Our synthesis provides the most comprehensive experimental test of the WSWH to date and shows that warming can elevate infection risk while generating heterogeneous outcomes among host-parasite systems.

ecology↗

bioRxiv2025

Parasite-mediated inbreeding depression in wild red deer

Inbreeding depression is the reduction in fitness of inbred individuals relative to their more outbred counterparts. Parasitism also reduces fitness and is a route by which inbreeding depression may operate, yet the complete pathway from inbreeding to parasitism to fitness has almost never been documented in the wild. Using high-quality, individual-level data on fitness in juveniles and adult females, longitudinal infection data for three gastrointestinal helminth parasites, and genomic inbreeding coefficients we test for parasite-mediated inbreeding depression in a wild ungulate population (red deer, Cervus elaphus). We found evidence for parasite-mediated inbreeding depression via strongyle nematodes in juvenile survival, independent of direct adverse effects of inbreeding on survival and indirect effects of inbreeding on survival via birth weight. Inbreeding also reduced fitness in reproductive adults by reducing overwinter survival. Our study reveals three independent pathways by which inbreeding depresses fitness and highlights the rarely-studied route of parasitism.

ecology↗

bioRxiv2024

Population density drives increased parasitism via greater exposure and reduced resource availability in wild hosts

Exposure to environmental parasites should increase with host population density due to the accumulation of infective parasites in space. However, competition for resources also increases with density, lowering condition and increasing susceptibility, which offers an alternative pathway for density-dependent infection to act. To test how these two processes act independently or together to drive greater parasite counts, we used a long-term study of red deer to examine associations between host density, resource availability, and counts of three common helminth parasites. We found that greater density correlated with reduced resource availability, and while density was positively associated with both strongyle and tissue worm burdens, resource availability was independently and negatively associated with the same burdens, supporting separate roles of density-dependent exposure and susceptibility in driving infection. This study provides evidence that competition for resources is an important driver of infection in higher-density areas, exacerbating the effects of density-dependent increases in exposure.

ecology↗

bioRxiv2024

Parasite contingency loci and the evolution of host specificity: Simple sequence repeats mediate Bartonella adaptation to a wild rodent host

Parasites can adapt to better exploit their hosts on many scales, ranging from within an infection of a single individual to series of infections spanning multiple host species. However, little is known about how the genomes of parasites in natural communities evolve when they face diverse hosts. We investigated how Bartonella bacteria that circulate in rodent communities in the dunes of the Negev Desert in Israel adapt to different species of rodent hosts. We propagated 15 Bartonella populations through infections of either a single host species (Gerbillus andersoni or Gerbillus pyramidum) or alternating between the two. After 20 rodent passages, strains with de novo mutations replaced the ancestor in most populations. Mutations in two mononucleotide simple sequence repeats (SSRs) that caused frameshifts in the same adhesin gene dominated the evolutionary dynamics. They appeared exclusively in populations that encountered G. andersoni and altered the dynamics of infections of this host. Similar SSRs in other genes are conserved and exhibit ON/OFF variation in Bartonella isolates from the Negev Desert dunes. Our results suggest that SSR-based contingency loci could be important not only for rapidly and reversibly generating antigenic variation to escape immune responses but that they may also mediate the evolution of host specificity.

evolutionary biology↗