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Ecology of Free-ranging Axis Deer (Axis axis) in the Edwards Plateau Ecoregion of Central Texas: Population Density, Genetics, and Impacts of an Invasive Deer Species

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... Point independence was again assumed. Deer were placed in one of six age categories (<1, 1-2.5, 2.5-4, 4-6, 6-8 and ≥8 years old) determined from tooth eruption and wear (Buchholz 2022) in the laboratory by the same observer. Tooth eruption indicates deer age up to 3 years old in chital deer (Graf and Nichols 1966;Buchholz 2022), but tooth wear tends to underestimate the true age of older animals particularly ≥6 years old (Foley et al. 2022). ...
... Deer were placed in one of six age categories (<1, 1-2.5, 2.5-4, 4-6, 6-8 and ≥8 years old) determined from tooth eruption and wear (Buchholz 2022) in the laboratory by the same observer. Tooth eruption indicates deer age up to 3 years old in chital deer (Graf and Nichols 1966;Buchholz 2022), but tooth wear tends to underestimate the true age of older animals particularly ≥6 years old (Foley et al. 2022). Factors such as location, diet and observer biases are believed to influence deer age estimated from tooth wear, but the influence can be minor (Hamlin et al. 2000;Foley et al. 2022). ...
... Factors such as location, diet and observer biases are believed to influence deer age estimated from tooth wear, but the influence can be minor (Hamlin et al. 2000;Foley et al. 2022). For Texan chital deer, Buchholz (2022) found deer age in ≥2-year age groupings determined by tooth eruption and wear matched ages determined by cementum annuli, which is regarded as the most accurate measure available (Hamlin et al. 2000;Foley et al. 2022), and that tooth wear did not differ between the sexes. For this study, deer were sampled from the same geographic area, animals ≥8 years old were placed in a single age class and age was used as a relative rather than an absolute measure in comparisons between the sexes. ...
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Context Chital deer (Axis axis) are long established in the northern Queensland dry tropics, and at high densities are considered pests by cattle graziers. Cost-effective management is difficult for widespread, fluctuating populations of vertebrate pests such as these deer. Historically, control of chital deer has been limited to recreational and some commercial ground-shooting and trapping. Concerns over chital deer impacts were heightened during drought in 2015 and funding became available for aerial culling. Aim This study set out to determine (1) distribution and abundance, (2) seasonal reproductive output, (3) potential and actual rates of increase and their determinants, and (4) efficient management strategies for chital deer in the northern Queensland dry tropics. Methods In 2014, ~13 000 km2 of the main distribution was surveyed by helicopter. Multiple vehicle ground surveys per year monitored chital deer density on two properties during 2013–2022. Seasonal shot samples of deer on both properties assessed reproductive output during 2014–2016. Aerial surveys during 2016–2020 determined chital deer densities on seven properties, prior to aerial culling on four properties. Finally, the maximum rate of increase of chital deer was calculated from life-history data. Key results Regionally, chital deer are patchily distributed and so are best monitored locally where densities can be >50 deer km−2. Vehicle ground surveys recorded an ~80% decline in chital deer populations on two properties over 7–10 months during drought in early 2015, with a similar rate being recorded by aerial survey at a third site. There was little recruitment during the drought, but the decline was seemingly driven by adult mortality. Aerial shooting further reduced populations by 39–88% to <3 deer km−2 on four properties. Where there was no continuing control, culled populations recovered to pre-cull densities or higher after 2.4 years. One unculled property recovered to its pre-drought density after 6 years. Rates of recovery were at or higher than the maximum annual rate of increase for chital deer estimated here as 26–41%. Conclusions Drought has a lasting effect on this chital deer population, because of the resulting large population decline and the modest rate of any recovery in the absence of culling. Culling can reduce populations to low density, but the removal rate needs to be sustained to suppress future growth. Implications Drought provides a strategic opportunity to further reduce chital deer populations for enduring control. Large reductions are feasible given the clumped dispersion of populations within properties and in the region.
... However, the introductions were often conducted with very minimal understanding of potential ecological impacts. These free-ranging populations can have substantial negative impacts on the ecology and socioeconomic benefits of native ecosystems including changing composition of vegetation communities and affecting viability of livestock husbandry (Hess 2008;Nentwig et al. 2018;Buchholz 2022). ...
... For instance, the number and sex ratio of the founding individuals introduced to Texas in 1932 are unknown. Additionally, records indicate that axis deer were introduced into just one county in Texas (Kerr County) but have since spread to at least 34 counties as free-ranging individuals (and over 100 counties as captive individuals) with an estimate of ~61,000 individuals in Kimble County, Texas, alone (Buchholz 2022). In Hawaii, on the islands of Maui, Molokai, and Lanai, the entire population is reported to be descended from only eight deer that were introduced to Molokai in 1867 and with descendants later introduced to the other islands (Cooke 1949;Graf and Nichols 1966). ...
... Ultimately, the potential loss of genetic diversity during the bottleneck and possibility of inbreeding do not seem to have negatively impacted axis deer in either Texas or Hawaii-both populations are thriving and not demonstrating negative signs of low genetic diversity that would manifest as physical malformities or reduced reproductive success (Hess and Judge 2021;Buchholz 2022). A possible explanation for the success of axis deer with low genetic diversity in introduced ranges is that they may have started with beneficial adaptive, rather than harmful maladaptive, genotypes and any trend toward fixation of those traits via genetic drift has aided the population as a whole (Barbosa 2021). ...
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Human-mediated introductions and subsequent establishment and spread of nonnative species have the potential to create a founder effect in such populations, which typically results in low genetic diversity and potential for inbreeding. However, several exotic invasive species exhibit a “genetic paradox” in which they thrive and adapt to novel environments while also avoiding complications from low genetic diversity. Axis deer (Axis axis) were introduced into Texas, Hawaii, South America, Australia, and Croatia during the 19th and 20th centuries and successfully established large populations from a few founding individuals. Mitochondrial (Cytochrome-b, Cytb; displacement loop, D-loop) and nuclear (10 microsatellites) markers were used to assess genetic diversity within and between axis deer populations in Texas and Hawaii and then compared to other introduced (Australia and Croatia) and native (India) populations. Overall, mtDNA divergence was 0.54% (Cytb) and 1.55% (D-loop) indicating high mitochondrial similarity within the species. Further, each invasive population was composed of only one or two mtDNA haplotypes. Microsatellite allele diversity also was low within and between populations in Texas and Hawaii resulting in monomorphic loci and Hardy–Weinberg equilibrium violations in both populations. The low genetic diversity in native Indian axis deer and within and between invasive populations suggests that the introduced populations experienced founder effects following introduction, and yet overcame this potential handicap by undergoing successful establishment and expansion. Axis deer appear to be another successful invasive species characterized by the genetic paradox where they exhibit genetic profiles that suggest inbreeding effects should be imminent, yet display no signs of inbreeding and are highly successful adapting to novel environments.
... Several factors have likely contributed to the population growth of axis deer in the region during the~30 y. Reproductive traits including the ability of does to become pregnant every 9 mo (Ables 1977;Schmidly and Bradley 2016), year-round breeding potential of does (when not pregnant; Ables 1977; Schmidly and Bradley 2016), possible viability of sperm year-round regardless of antler status in bucks (Willard and Randel 2002), and longevity records in the state that suggest axis deer can live to !15 y old with pregnancy possible until !13 y old (see Buchholz 2022) have likely combined to support the rapid growth in axis deer abundance during the past 30þ y. Furthermore, as an introduced species, axis deer likely experience enemy release (see Blossey 2011). ...
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Axis deer Axis axis have been widely introduced to new geographic ranges and in the United States, free-ranging axis deer have become well established in the Edwards Plateau ecoregion as well as other portions of Texas. However, no estimates of axis deer population density or size have been conducted since 1994. It is hypothesized that axis deer on the Edwards Plateau are potentially competing with native white-tailed deer Odocoileus virginianus for food, space, and habitat resources, and causing damage to important riparian habitats. Our goal was to estimate regional densities of axis deer and white-tailed deer, and provide insight about the potential impacts axis deer may have on native wildlife and their habitats. Estimated using distance sampling techniques in 2018 and 2019, average axis deer density was 19.7 (95% CI: 14.1 – 25.6) axis deer/km2 compared to 23.0 (95% CI: 18.2 – 27.5) white-tailed deer/km2, and axis deer densities ranged from 16.9 – 171.0 /km2 among eight different land cover types in Kimble County, TX, with a county wide estimate of 61,078 (95% CI: 30,407 – 100,369) axis deer. Axis deer densities were greatest in riparian habitats, and they selected for two riparian habitats and upland grasslands. Axis deer population estimates clearly indicate their population size has increased substantially since introduction to Texas in the 1930’s. Population management of axis deer is warranted to limit impacts to native wildlife from potential habitat usurpation, or damage to riparian vegetation communities, soil, and water quality.
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The invasion of exotic species is considered one of the major causes of the current biodiversity crisis. Exotic ungulates are the world’s most intentionally introduced vertebrates. The axis deer is native to Asia and was successfully introduced in different regions of the world. In South America this deer was initially recorded in Argentina and Uruguay; in Brazil the species has been reported from two states, Rio Grande do Sul and Santa Catarina State. Here we describe the first record of Axis axis at the border of Iguaçu National Park, Paraná State, southern Brazil. This new record indicates a rapid and concerning increase of the species’ distribution in Brazil. Further assessments of axis deer in Paraná State are necessary to evaluate the current situation and generate data to support the elaboration of a strategy to manage and control the species in the region, as it represents a threat to the local biodiversity
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Elk (Cervus canadensis) historically are among the most widely distributed members of the deer family, occupying much of the United States, Canada, and northern Mexico. The natural distribution of this species decreased substantially in the early 20 th century, presumably resulting in the extirpation of populations in Texas. In the past 40 years, several herds of free-ranging elk have reappeared in the Trans-Pecos region of Texas. For some herds, it is not known if the origin was: 1) the result of individuals that escaped from captive herds; 2) an expansion of previously transplanted individuals from South Dakota and Oregon into Texas; or 3) the result of natural emigrants from southeastern New Mexico into the Trans-Pecos region. The objective of this study was to use DNA sequences from the mitochondrial cytochrome-b gene and D-Loop region, in combination with nine microsatellite loci, to assess genetic divergence, relationships, and origin(s) of the contemporary elk herds in Texas. Findings of the mitochondrial sequence data depicted a high degree of relatedness among individuals throughout the sampling area; whereas, microsatellite data revealed differences in frequencies of alleles in the Glass Mountain populations of Texas compared to samples from South Dakota, New Mexico, and the Davis Mountains. Further, computer simulations of population genetic parameters based on the mi-crosatellite data supported a scenario depicting the origin of contemporary elk in Texas likely was the result of natural emigrants from New Mexico or descendants of previously introduced individuals from New Mexico. In addition, simulations did not detect evidence of a genetic bottleneck during the past 350 generations, indicating a long, shared history between Texas and New Mexico populations.
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The axis deer (Axis axis) is a species of ungulate native to the Indian subcontinent. In the 19th and 20th centuries, the axis deer was introduced to many regions of the world, where it established non-native free-ranging populations. The introduction of the axis deer to Croatia resulted in three populations that still live on the Adriatic islands. In this study, two new mitochondrial DNA control region (D-loop) haplotypes were identified in 39 axis deer samples from two Adriatic islands Rab and Dugi Otok in Croatia. Two distinct D-loop haplotypes found in Croatian axis deer populations indicate that axis deer in Croatia were introduced from at least two maternal lineages. Genetic differentiation between populations was quite low and not significant. Haplotype (0.497) and nucleotide (0.006) diversity of Croatian axis deer was similar to that of axis deer from Queensland, Australia (0.461 and 0.002, respectively). For a better understanding of the origin and genetic diversity of the introduced axis deer from Croatia, analysis of native populations and the addition of highly variable nuclear markers is required.
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Axis axis (Erxleben, 1777) is an Old World deer commonly known as chital, Indian spotted deer, or axis deer. It is one of five species in the genus Axis and is native to the Indian subcontinent, occurring in India, Nepal, Bhutan, Bangladesh, and Sri Lanka. Free-ranging and confined populations of A. axis have been established in Europe, Australia, and both North and South America. Globally, it is considered “Least Concern” (LC) by the International Union for Conservation of Nature and Natural Resources.
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PrP C variation at residue 96 (G/S) plays an important role in the epidemiology of chronic wasting disease (CWD) in exposed white-tailed deer populations. In vivo studies have demonstrated the protective effect of serine at codon 96, which hinders the propagation of common CWD strains when expressed in homozygosis and increases the survival period of S96/wt heterozygous deer after challenge with CWD. Previous in vitro studies of the transmission barrier suggested that following a single amplification step, wt and S96 PrP C were equally susceptible to misfolding when seeded with various CWD prions. When we performed serial prion amplification in vitro using S96-PrP C , we observed a reduction in the efficiency of propagation with the Wisc-1 or CWD2 strains, suggesting these strains cannot stably template their conformations on this PrP C once the primary sequence has changed after the first round of replication. Our data shows the S96-PrP C polymorphism is detrimental to prion conversion of some CWD strains. These data suggests that deer homozygous for S96-PrP C may not sustain prion transmission as compared to a deer expressing G96-PrP C .
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