Seasonal Variation in Sex Ratios Provides Developmental Advantages in White-tailed Deer, Odocoileus virginianus

Since Trivers and Willard first proposed their hypothesis concerning the adaptive advantages of producing a particular offspring sex in relation to maternal condition in 1973, it has been at the forefront of scientific research concerning sex ratios with most subsequent studies focusing on maternal condition as a key contributor to variations in sex ratios. Another factor that could greatly influence sex ratios, although has been only infrequently examined in mammalian species, is birth date. We investigated how birth date influenced offspring sex ratios in White-tailed Deer (Odocoileus virginianus). Since date of birth can greatly influence an individual’s fitness and reproductive success, we suggest that birth date may be an alternative strategy in determining offspring sex ratios. Since it has been shown that the lifetime reproductive fitness of a mother can be increased by producing a particular sex during a particular time, we hypothesized that more male offspring should be born earlier in the season due to their increased reproductive potential from being born at this time. Offspring born earlier will have a head start in development and therefore have greater potential for increased body size and dominance later in life, traits that greatly influence male reproductive success. In this study, we found that maternal condition did not affect offspring sex ratio in a captive population of White-tailed Deer in Michigan; however, birth date did. We found that more males tended to be born during the second and fourth birthing periods, while more females were born during the first, third and fifth periods. In addition, we found that males born earlier in the season had greater mass the following spring than those born later, a trend that was not as dramatic in females. These results lend moderate support to our hypothesis that in White-tailed Deer offspring sex will tend to vary according to timing of birth and relative reproductive advantages gained by a particular sex being born at that time

A review of the impacts of invasive wild pigs on native vertebrates

The wild pig (Sus scrofa) is a successful invasive species that has become well established outside of its native range in Eurasia. The invasive wild pig is the result of released or escaped domesticated livestock becoming feral, or Eurasian boar introduced for hunting purposes. The global spread of wild pigs has recently been exacerbated in some areas, such as the USA, by anthropogenically assisted dispersal. Once established in novel ecosystems, wild pigs have the potential to have significant negative impacts on the ecosystem, and the scientific literature is replete with examples. It is generally accepted that wild pigs negatively impact native fauna where they have become established, yet the degree to which they impact faunal communities has not been well described. This paper serves as a review of the information to date on the implications of wild pig invasions and impacts they have on terrestrial vertebrates in their invasive range. In addition, the review highlights our need for more research in this area, particularly regarding declining species

Wild pig removal reduces pathogenic bacteria in low-order streams

Invasive wild pig populations have undergone enormous increases in the United States and particularly across the southern U.S. in recent years. High fecundity rates and abilities to adapt quickly to varied habitats have enabled pig populations to become entrenched and difficult to eliminate. The pigs cause many negative impacts on ecosystems including degradation of water quality through infusion of fecal contamination and other non-point source pollutants. Our goal was to determine the effects of pig removal on water quality in streams that were known to be significantly polluted by pig activity Bolds (J Environ Qual 50: 441–453, 2021). We compared e. coli and fecal coliform concentrations and loads in streams between a pre-removal period with those that occurred during the removal activities. Results suggest that e. coli and fecal coliform concentrations were reduced by 75 and 50% respectively through pig removal efforts. Questions remain concerning the longevity of the reduction especially once pig removal activities decrease in intensity

Transmission of bovine viral diarrhea virus among white-tailed deer (Odocoileus virginianus)

Cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV), a pestivirus in the family Flaviviridae, are an important source of viral transmission to susceptible hosts. Persistent BVDV infections have been identified in white-tailed deer (Odocoileus virginianus), the most abundant free-ranging ruminant in North America. As PI deer shed BVDV similarly to PI cattle, maintenance of BVDV within white-tailed deer populations may be possible. To date, intraspecific transmission of BVDV in white-tailed deer has not been evaluated, which prompted this study. Six pregnant white-tailed deer were captured in the first trimester of pregnancy and cohabitated with a PI white-tailed deer. Cohabitation with the PI deer resulted in BVDV infection in all does, as indicated by seroconversion. All does gave birth to live fawns and no reproductive losses were observed. At birth, evidence of BVDV infection was identified in two singlet fawns, of which one was determined to be PI by repeated serum reverse transcription nested PCR, whole blood virus isolation and immunohistochemistry. This study demonstrates for the first time that BVDV transmission may occur among white-tailed deer. The birth of a PI fawn through contact to a PI white-tailed deer indicates that under appropriate circumstances, BVDV may be maintained in white-tailed deer by congenital infection

Predicting functional responses in agro-ecosystems from animal movement data to improve management of invasive pests

Functional responses describe how changing resource availability affects con- sumer resource use, thus providing a mechanistic approach to prediction of the invasibility and potential damage of invasive alien species (IAS). However, functional responses can be context dependent, varying with resource characteristics and availability, consumer attributes, and environmental variables. Identifying context dependencies can allow invasion and damage risk to be predicted across different ecoregions. Understanding how ecological factors shape the functional response in agro-ecosystems can improve predictions of hotspots of highest impact and inform strategies to mitigate damage across locations with varying crop types and avail- ability. We linked heterogeneous movement data across different agro-ecosystems to predict ecologically driven variability in the functional responses. We applied our approach to wild pigs (Sus scrofa), one of the most successful and detrimental IAS worldwide where agricultural resource depredation is an important driver of spread and establishment. We used continental- scale movement data within agro-ecosystems to quantify the functional response of agricul- tural resources relative to availability of crops and natural forage. We hypothesized that wild pigs would selectively use crops more often when natural forage resources were low. We also examined how individual attributes such as sex, crop type, and resource stimulus such as dis- tance to crops altered the magnitude of the functional response. There was a strong agricul- tural functional response where crop use was an accelerating function of crop availability at low density (Type III) and was highly context dependent. As hypothesized, there was a reduced response of crop use with increasing crop availability when non-agricultural resources were more available, emphasizing that crop damage levels are likely to be highly heterogeneous depending on surrounding natural resources and temporal availability of crops. We found sig- nificant effects of crop type and sex, with males spending 20% more time and visiting crops 58% more often than females, and both sexes showing different functional responses depend- ing on crop type. Our application demonstrates how commonly collected animal movement data can be used to understand context dependencies in resource use to improve our under- standing of pest foraging behavior, with implications for prioritizing spatiotemporal hotspots of potential economic loss in agro-ecosystems

Host Reproductive Phenology Drives Seasonal Patterns of Host Use in Mosquitoes

Seasonal shifts in host use by mosquitoes from birds to mammals drive the timing and intensity of annual epidemics of mosquito-borne viruses, such as West Nile virus, in North America. The biological mechanism underlying these shifts has been a matter of debate, with hypotheses falling into two camps: (1) the shift is driven by changes in host abundance, or (2) the shift is driven by seasonal changes in the foraging behavior of mosquitoes. Here we explored the idea that seasonal changes in host use by mosquitoes are driven by temporal patterns of host reproduction. We investigated the relationship between seasonal patterns of host use by mosquitoes and host reproductive phenology by examining a seven-year dataset of blood meal identifications from a site in Tuskegee National Forest, Alabama USA and data on reproduction from the most commonly utilized endothermic (white-tailed deer, great blue heron, yellow-crowned night heron) and ectothermic (frogs) hosts. Our analysis revealed that feeding on each host peaked during periods of reproductive activity. Specifically, mosquitoes utilized herons in the spring and early summer, during periods of peak nest occupancy, whereas deer were fed upon most during the late summer and fall, the period corresponding to the peak in births for deer. For frogs, however, feeding on early- and late-season breeders paralleled peaks in male vocalization. We demonstrate for the first time that seasonal patterns of host use by mosquitoes track the reproductive phenology of the hosts. Peaks in relative mosquito feeding on each host during reproductive phases are likely the result of increased tolerance and decreased vigilance to attacking mosquitoes by nestlings and brooding adults (avian hosts), quiescent young (avian and mammalian hosts), and mate-seeking males (frogs)

Ecology and management of feral hogs

Feral hogs (Sus scrofa) have been present in North America since the arrival of the earliest settlers in the sixteenth century. Colonists originally released hogs because of the animals’ ability to survive on their own and to serve as a ready food supply for settlers. Since that time, hogs have expanded their range and now are present in 40 of the 50 United States and parts of Canada. Their rapid expansion is similar to that of other introduced species, and, as a result, they are generally classified as an invasive exotics, along with hundreds of other plant and animal species. However, feral hogs may pose an ecological threat that far surpasses that posed by other invasive vertebrates