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Scott ME. Helminth-host-environment interactions: Looking down from the tip of the iceberg. J Helminthol 2023; 97:e59. [PMID: 37486085 DOI: 10.1017/s0022149x23000433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/25/2023]
Abstract
In 1978, the theory behind helminth parasites having the potential to regulate the abundance of their host populations was formalized based on the understanding that those helminth macroparasites that reduce survival or fecundity of the infected host population would be among the forces limiting unregulated host population growth. Now, 45 years later, a phenomenal breadth of factors that directly or indirectly affect the host-helminth interaction has emerged. Based largely on publications from the past 5 years, this review explores the host-helminth interaction from three lenses: the perspective of the helminth, the host, and the environment. What biotic and abiotic as well as social and intrinsic host factors affect helminths? What are the negative, and positive, implications for host populations and communities? What are the larger-scale implications of the host-helminth dynamic on the environment, and what evidence do we have that human-induced environmental change will modify this dynamic? The overwhelming message is that context is everything. Our understanding of second-, third-, and fourth-level interactions is extremely limited, and we are far from drawing generalizations about the myriad of microbe-helminth-host interactions.Yet the intricate, co-evolved balance and complexity of these interactions may provide a level of resilience in the face of global environmental change. Hopefully, this albeit limited compilation of recent research will spark new interdisciplinary studies, and application of the One Health approach to all helminth systems will generate new and testable conceptual frameworks that encompass our understanding of the host-helminth-environment triad.
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Affiliation(s)
- M E Scott
- Institute of Parasitology, McGill University (Macdonald Campus), 21,111 Lakeshore Road, Ste-Anne de Bellevue, QuebecH9X 3V9, Canada
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2
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Vedel G, de la Peña E, Moreno-Rojas JM, Carranza J. Is the Intrasexual Competition in Male Red Deer Reflected in the Ratio of Stable Isotopes of Carbon and Nitrogen in Faeces? Animals (Basel) 2023; 13:2397. [PMID: 37508173 PMCID: PMC10375991 DOI: 10.3390/ani13142397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Revised: 07/12/2023] [Accepted: 07/18/2023] [Indexed: 07/30/2023] Open
Abstract
Isotopic analysis of carbon and nitrogen in faeces is a reliable methodology for studying ecology in wildlife. Here, we tested this technique to detect variations in carbon and nitrogen isotopic ratios (δ13C and δ15N) in two different intrasexual competition scenarios of male Iberian red deer (Cervus elaphus hispanicus) using faeces of individuals collected during hunting actions in South-eastern Spain. The carbon isotopic ratio (δ13C) was not found to be significant, likely due to similar diet composition in all individuals. However, the nitrogen isotopic ratio (δ15N) was found to be lower in populations where sexual competition between males during the rut was higher compared to low-competition populations. Therefore, this study suggests a different use of proteins by an individual male red deer depending on the sexually competitive context in which he lives. Although further research is needed, these results show the potential of isotopic analysis as a tool for studying individual and populational variations in the level of intrasexual competition, with implications in evolutionary ecology and population management.
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Affiliation(s)
- Giovanni Vedel
- Wildlife Research Unit (UiRCP), University of Córdoba, 14071 Córdoba, Spain
| | - Eva de la Peña
- Wildlife Research Unit (UiRCP), University of Córdoba, 14071 Córdoba, Spain
- Instituto de Investigación en Recursos Cinegéticos, IREC (CSIC, UCLM, JCCM), Ronda de Toledo 12, 13005 Ciudad Real, Spain
| | - Jose Manuel Moreno-Rojas
- Department of Agroindustry and Food Quality, Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA), Alameda del Obispo. Avda. Menéndez Pidal, s/n., 14071 Córdoba, Spain
| | - Juan Carranza
- Wildlife Research Unit (UiRCP), University of Córdoba, 14071 Córdoba, Spain
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3
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Seasonal output of gastrointestinal nematode eggs and lungworm larvae in farmed wapiti and red deer of New Zealand. Vet Parasitol 2022; 303:109660. [DOI: 10.1016/j.vetpar.2022.109660] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 01/07/2022] [Accepted: 01/15/2022] [Indexed: 10/19/2022]
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4
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Holt WV, Comizzoli P. Opportunities and Limitations for Reproductive Science in Species Conservation. Annu Rev Anim Biosci 2021; 10:491-511. [PMID: 34699258 DOI: 10.1146/annurev-animal-013120-030858] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Reproductive science in the context of conservation biology is often understood solely in terms of breeding threatened species. Although technologies developed primarily for agriculture or biomedicine have a potentially important role in species conservation, their effectiveness is limited if we regard the main objective of animal conservation as helping to support populations rather than to breed a small number of individuals. The global threats facing wild species include the consequences of climate change, population growth, urbanization, atmospheric and water pollution, and the release of chemicals into the environment, to cite but a few. Reproductive sciences provide important and often unexpected windows into many of these consequences, and our aim here is both to demonstrate the breadth of reproductive science and the importance of basic knowledge and to suggest where some of the insights might be useful in mitigating the problems. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- William V Holt
- Academic Unit of Reproductive and Developmental Medicine, Department of Oncology & Metabolism, University of Sheffield, Sheffield, United Kingdom;
| | - Pierre Comizzoli
- Smithsonian Conservation Biology Institute, National Zoological Park, Washington, DC, USA;
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5
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de Araújo Albuquerque LP, da Silva AM, de Araújo Batista FM, de Souza Sene I, Costa DL, Costa CHN. Influence of sex hormones on the immune response to leishmaniasis. Parasite Immunol 2021; 43:e12874. [PMID: 34309860 DOI: 10.1111/pim.12874] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 06/23/2021] [Accepted: 07/06/2021] [Indexed: 12/11/2022]
Abstract
The differences in morbidity and mortality patterns and life expectancy between the sexes are well established in different infectious and parasitic conditions, such as in leishmaniases, in which biological, genetic, sexual and hormonal variations can modulate the immune response indicating greater infectivity, prevalence and clinical severity in men. In this regard, in seeking the understanding of factors related to protection and susceptibility to infection, this review aimed to discuss the influence of sex hormones on the immune response to leishmaniases. In the literature, sex hormone variations promote differences in the innate, humoral and cell-mediated immune response, leading to greater susceptibility, mortality and complications in males. Epidemiological estimates confirm these results, showing a predominance of the disease, in its different clinical forms, in men and suggesting that sexual variations influence immunomodulatory mechanisms since the prevalence of cases comprises the post-puberty and adulthood period. In this perspective, the action of sex hormones has been investigated in different clinical models, highlighting the potential of testosterone in immunosuppression, given its association with greater susceptibility and poor control of parasite load and the induction of cell apoptosis and attenuation of pro-inflammatory signalling pathways. Therefore, hormonal variations influence the immune response among males and females against leishmaniases, in which androgens may present immunosuppressive potential, while steroids present immunomodulatory characteristics.
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Affiliation(s)
| | - Amanda Miranda da Silva
- Postgraduate Program in Biotechnology, Northeast Network of Biotechnology, Federal University of Piauí, Teresina, Brazil.,Leishmaniasis Laboratory, Federal University of Piauí, Teresina, Brazil
| | | | | | - Dorcas Lamounier Costa
- Maternal and Child Department, Federal University of Piauí and Intelligence Center in Emerging and Neglected Tropical Conditions (CIATEN, Teresina, Brazil
| | - Carlos Henrique Nery Costa
- Community Medicine Department, Federal University of Piauí and Intelligence Center in Emerging and Neglected Tropical Conditions (CIATEN, Teresina, Brazil
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6
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de la Peña E, Pérez-González J, Martín J, Vedel G, Carranza J. The dark-ventral-patch of male red deer, a sexual signal that conveys the degree of involvement in rutting behavior. BMC ZOOL 2021; 6:18. [PMID: 37170131 PMCID: PMC10127101 DOI: 10.1186/s40850-021-00083-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 05/06/2021] [Indexed: 11/10/2022] Open
Abstract
Abstract
Background
In polygynous mammals, signalling may play a decisive role in mating behavior, mediating the intensity of male fights and female mate choice. During the rutting season, male red deer may show a visible dark patch in their ventral fur. Recently, this patch has been suggested to act as a flexible sexual signal, due to its relationships with other variables such as age, body size, antler development, volatile compounds, or the competitive environment. The analysis of fur pigmentation at the ventral patch suggests that this might also visually indicate the male intrinsic predisposition to take part in mating competition.
Results
To assess the possible role of this trait as a communicative signal related to mate competition, we used red deer behavioral observations during the rut in Doñana National Park (Spain) to examine the link between the degree of expression of the dark ventral patch and the rutting activity (assessed from both intra-and-inter-sexual behaviors). Consistent with our predictions, we found in a field study that males with large dark patches showed a higher frequency of rutting behaviors (mainly roaring and flehmen), more interactions with females, and attained larger harem sizes.
Conclusions
The dark ventral patch was a better predictor of male behavior than antler tines or territory holding, thus standing as a short-term indicator of male willingness to invest in mating competition.
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Xu S, Zhang S, Hu X, Zhang B, Yang S, Hu X, Liu S, Hu D, Bai J. Temporal and spatial dynamics of gastrointestinal parasite infection in Père David's deer. PeerJ 2021; 9:e11335. [PMID: 33996283 PMCID: PMC8106392 DOI: 10.7717/peerj.11335] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2020] [Accepted: 04/01/2021] [Indexed: 11/20/2022] Open
Abstract
Background The Père David's deer (Elaphurus davidianus) population was established from only a small number of individuals. Their genetic diversity is therefore relatively low and transmissible (parasitic) diseases affecting them merit further attention. Parasitic infections can affect the health, survival, and population development of the host. However, few reports have been published on the gastrointestinal parasites of Père David's deer. The aims of this study were: (1) to identify the intestinal parasites groups in Père David's deer; (2) to determine their prevalence and burden and clarify the effects of different seasons and regions on various indicators of Père David's deer intestinal parasites; (3) to evaluate the effects of the Père David's deer reproductive period on these parasites; (4) to reveal the regularity of the parasites in space and time. Methods In total, 1,345 Père David's deer faecal samples from four regions during four seasons were tested using the flotation (saturated sodium nitrate solution) to identify parasites of different genus or group, and the McMaster technique to count the number of eggs or oocysts. Results Four groups of gastrointestinal parasites were found, of which strongyles were dominant; their prevalence and burden were significantly higher than other groups. Significant temporal and spatial effects on gastrointestinal parasitic infection were found. Parasite diversity, prevalence, parasite burden, and aggregation were the highest in summer. Among the four regions, parasite diversity, prevalence, and burden were the highest in the Dongting Lake area. In addition, parasite diversity and burden during the reproductive period of Père David's deer was significantly higher than during the post-reproductive period. Conclusions The summer season and the reproductive period of Père David's deer had great potential for parasite transmission, and there is a high risk of parasite outbreaks in the Dongting Lake area.
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Affiliation(s)
- Shanghua Xu
- School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, China
| | - Shumiao Zhang
- Department of Research, Beijing Milu Ecological Research Center, Beijing, China
| | - Xiaolong Hu
- College of Animal Science and Technology, Jiangxi Agricultural University, Nanchang, Jiangxi, China
| | - Baofeng Zhang
- School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, China
| | - Shuang Yang
- School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, China
| | - Xin Hu
- Beijing Key Laboratory of Captive Wildlife Technologies, Beijing Zoo, Beijing, China
| | - Shuqiang Liu
- School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, China
| | - Defu Hu
- School of Ecology and Nature Conservation, Beijing Forestry University, Beijing, China
| | - Jiade Bai
- Department of Research, Beijing Milu Ecological Research Center, Beijing, China
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8
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de la Peña E, Barja I, Carranza J. Social environment with high intrasexual competition enhances the positive relationship between faecal testosterone and cortisol metabolite levels in red deer. Mamm Biol 2021. [DOI: 10.1007/s42991-021-00100-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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9
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Brandimarti ME, Gray R, Hilton ZJ, Keeley T, Murray ‘KP, Herbert CA. The effect of testosterone suppression on health and parasite burden in male eastern grey kangaroos (Macropus giganteus). AUSTRALIAN MAMMALOGY 2021. [DOI: 10.1071/am21017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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10
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Carranza J, de la Peña E, Mateos C, Pérez-González J, Alarcos S, Torres-Porras J, Valencia J, Sánchez-Prieto C, Castillo L. The dark ventral patch: A bimodal flexible trait related to male competition in red deer. PLoS One 2020; 15:e0241374. [PMID: 33151970 PMCID: PMC7644014 DOI: 10.1371/journal.pone.0241374] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Accepted: 10/13/2020] [Indexed: 11/29/2022] Open
Abstract
Sexual signals play a central role in male-male competition in polygynous species. In red deer (Cervus elaphus), male's ventral area become dark during the rutting season due to urine spraying behaviour and retains many chemical compounds potentially revealing individual features. Here we investigate the variation in size of this trait, exploring its relationship with age and male competitive features such as antlers or body size, as well as populational level of intrasexual competition for mates. We found that the size of the dark ventral patch followed a clearly bimodal distribution, i.e. males mostly expressed the full-size trait or just developed a very small one. For these two groups of males according to trait expression, the relationships of trait size with age and antler size differed. Populational level of intrasexual competition appeared to affect the relationship between antler size and the probability of a fully developed ventral patch. These results indicate that the trait encodes information on body size, antler size, age and populational level of mate competition, thus suggesting a role in signalling male's competitive features and willingness to allocate reproductive effort within a particular season.
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Affiliation(s)
- Juan Carranza
- Wildlife Research Unit (UiRCP), University of Córdoba, Córdoba, Spain
| | - Eva de la Peña
- Wildlife Research Unit (UiRCP), University of Córdoba, Córdoba, Spain
| | - Concha Mateos
- Biology & Ethology, University of Extremadura, Cáceres, Spain
| | | | - Susana Alarcos
- Biology & Ethology, University of Extremadura, Cáceres, Spain
| | - Jerónimo Torres-Porras
- Department of Social and Experimental Sciences Teaching, Faculty of Educational Sciences, University of Córdoba, Córdoba, Spain
| | - Juliana Valencia
- Experimental Sciences Teaching, Faculty of Educational Sciences, University of Málaga, Málaga, Spain
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11
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Peña E, Martín J, Carranza J. Ultrastructural morphological features of the hair in a sexual signal: the dark ventral patch of male red deer. J Zool (1987) 2020. [DOI: 10.1111/jzo.12833] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- E. Peña
- Wildlife Research Unit (UIRCP) University of Córdoba Córdoba Andalucía Spain
| | - J. Martín
- Department of Evolutionary Ecology Museo Nacional de Ciencias Naturales (MNCN‐CSIC) Madrid Spain
| | - J. Carranza
- Wildlife Research Unit (UIRCP) University of Córdoba Córdoba Andalucía Spain
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12
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Carranza J, Pérez-Barbería J, Mateos C, Alarcos S, Torres-Porras J, Pérez-González J, Sánchez-Prieto CB, Valencia J, Castillo L, de la Peña E, Barja I, Seoane JM, Reglero MM, Flores A, Membrillo A. Social environment modulates investment in sex trait versus lifespan: red deer produce bigger antlers when facing more rivalry. Sci Rep 2020; 10:9234. [PMID: 32514059 PMCID: PMC7280183 DOI: 10.1038/s41598-020-65578-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 05/04/2020] [Indexed: 11/23/2022] Open
Abstract
Theory predicts that the plastic expression of sex-traits should be modulated not only by their production costs but also by the benefits derived from the presence of rivals and mates, yet there is a paucity of evidence for an adaptive response of sex-trait expression to social environment. We studied antler size, a costly and plastic sex trait, and tooth wear, a trait related to food intake and longevity, in over 4,000 male Iberian red deer (Cervus elaphus hispanicus) from 56 wild populations characterized by two contrasting management practices that affect male age structure and adult sex-ratio. As a consequence, these populations exhibit high and low levels of male-male competition for mating opportunities. We hypothesized that males under conditions of low intra-sexual competition would develop smaller antlers, after controlling for body size and age, than males under conditions of high intra-sexual competition, thus reducing energy demands (i.e. reducing intake and food comminution), and as a consequence, leading to less tooth wear and a concomitant longer potential lifespan. Our results supported these predictions. To reject possible uncontrolled factors that may have occurred in the wild populations, we carried out an experimental design on red deer in captivity, placing males in separate plots with females or with rival males during the period of antler growth. Males living with rivals grew larger antlers than males living in a female environment, which corroborates the results found in the wild populations. As far as we know, these results show, for the first time, the modulation of a sexual trait and its costs on longevity conditional upon the level of intra-sexual competition.
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Affiliation(s)
- Juan Carranza
- Wildlife Research Unit (UIRCP), Universidad de Córdoba, 14071, Córdoba, Spain.
| | - Javier Pérez-Barbería
- Wildlife Research Unit (UIRCP), Universidad de Córdoba, 14071, Córdoba, Spain
- Game and Livestock Resources Unit, University of Castilla-La Mancha, IDR, IREC, Albacete, 02071, Spain
| | - Concha Mateos
- Biology and Ethology Unit, Universidad de Extremadura, 10071, Cáceres, Spain
| | - Susana Alarcos
- Biology and Ethology Unit, Universidad de Extremadura, 10071, Cáceres, Spain
| | - Jerónimo Torres-Porras
- Department of Social and Experimental Sciences Teaching, Faculty of Educational Sciences, Universidad de Córdoba, 14071, Córdoba, Spain
| | | | | | - Juliana Valencia
- Didáctica de las Ciencias Experimentales, Facultad de Ciencias de la Educación, Universidad de Málaga, Málaga, Spain
| | - Leticia Castillo
- Biology and Ethology Unit, Universidad de Extremadura, 10071, Cáceres, Spain
| | - Eva de la Peña
- Wildlife Research Unit (UIRCP), Universidad de Córdoba, 14071, Córdoba, Spain
| | - Isabel Barja
- Department of Biology, Zoology Unit, Universidad Autónoma (UAM), 28049, Madrid, Spain
- Biodiversity and Global Change Research Centre (CIBC-UAM), Universidad Autónoma (UAM), 28049, Madrid, Spain
| | - José M Seoane
- Wildlife Research Unit (UIRCP), Universidad de Córdoba, 14071, Córdoba, Spain
| | - Manuel M Reglero
- Gestión Cinegética Integral S.L. and Lagunes Selección Genética S.L., Madrid, Spain
| | - Antonio Flores
- Biology and Ethology Unit, Universidad de Extremadura, 10071, Cáceres, Spain
| | - Alberto Membrillo
- Wildlife Research Unit (UIRCP), Universidad de Córdoba, 14071, Córdoba, Spain
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Long-Term Determinants of Tuberculosis in the Ungulate Host Community of Doñana National Park. Pathogens 2020; 9:pathogens9060445. [PMID: 32516963 PMCID: PMC7350361 DOI: 10.3390/pathogens9060445] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 06/01/2020] [Accepted: 06/02/2020] [Indexed: 11/16/2022] Open
Abstract
Animal tuberculosis (TB) is endemic in wild boar (Sus scrofa), red deer (Cervus elaphus), fallow deer (Dama dama) and cattle in south and central Spain. In order to clarify the processes that operate in the medium and long-term, we studied TB at the wildlife–livestock interface in Doñana National Park for 14 years (2006–2018) in relation to host density, stochastic factors (rainfall) and environmental features (e.g., aggregation points such as waterholes). Wild boar showed the highest prevalence of TB (76.7%), followed by red deer (42.5%), fallow deer (14.4%) and cattle (10.7%). We found evidence of relevant epidemiological processes which operate over the long-term and interact with host and community ecology. Interestingly, the effect of high wild boar population density on increased TB rates was mediated by sows, which could determine high incidence in young individuals already in maternal groups. Rainfall significantly determined a higher risk of TB in male red deer, probably mediated by sex-related differences in life history traits that determined more susceptibility and/or exposure in comparison to females. The positive association between the prevalence of TB in fallow deer and cattle may indicate significant interspecies transmission (in either direction) and/or similar exposure to risk factors mediated by ecological overlapping of grazing species. The identification of long-term drivers of TB provided evidence that its control in extensive pastoral systems can only be achieved by targeting all relevant hosts and integrating measures related to all the factors involved, such as: population abundance and the aggregation of wild and domestic ungulates, environmental exposure to mycobacteria, cattle testing and culling campaigns and adjustments of appropriate densities.
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14
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Testosterone and the dark ventral patch of male red deer: the role of the social environment. Naturwissenschaften 2020; 107:18. [PMID: 32333124 DOI: 10.1007/s00114-020-01674-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 03/25/2020] [Accepted: 03/27/2020] [Indexed: 10/24/2022]
Abstract
The expression of male sexual traits, which is stimulated by testosterone, entails significant costs for individuals. Consequently, natural selection is expected to favour the modulation of sexual trait development according to the balance between its costs and benefits. The proportion of rivals in a population may affect this balance by increasing or decreasing the reproductive benefits associated with the development of sex traits. Here, we explore the relationship between testosterone level and sex trait size under two populational conditions of mate competition: fenced (i.e. high male-male competition; all male age groups are present) and unfenced (i.e. low competition; most males present are juveniles). Our model species is the Iberian red deer (Cervus elaphus hispanicus), and the sex trait is the dark ventral patch that males exhibit during the rutting season. Our results showed that the positive relationship between testosterone levels and the size of the dark ventral patch depends on the environmental level of male-male competition. Only in populations where the operational sex ratio was high (i.e. high proportion of rival males), individuals with high levels of testosterone developed the sex trait. Conversely, when mate competition was low, there was no significant relationship between testosterone level and trait size. This result reinforces the idea that the effect of testosterone in promoting the development of sex traits may be mediated by the intensity of mate competition in the population, as well as the role of sexual selection in the evolution of the dark ventral patch in red deer.
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