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PloS one2013; 8(1); e54972; doi: 10.1371/journal.pone.0054972

Contraception can lead to trophic asynchrony between birth pulse and resources.

Abstract: Abiotic inputs such as photoperiod and temperature can regulate reproductive cyclicity in many species. When humans perturb this process by intervening in reproductive cycles, the ecological consequences may be profound. Trophic mismatches between birth pulse and resources in wildlife species may cascade toward decreased survival and threaten the viability of small populations. We followed feral horses (Equus caballus) in three populations for a longitudinal study of the transient immunocontraceptive porcine zona pellucida (PZP), and found that repeated vaccinations extended the duration of infertility far beyond the targeted period. After the targeted years of infertility, the probability of parturition from post-treated females was 25.6% compared to 64.1% for untreated females, when the data were constrained only to females that had demonstrated fertility prior to the study. Estimated time to parturition increased 411.3 days per year of consecutive historical treatment. Births from untreated females in these temperate latitude populations were observed to peak in the middle of May, indicating peak conception occurred around the previous summer solstice. When the post-treated females did conceive and give birth, parturition was an estimated 31.5 days later than births from untreated females, resulting in asynchrony with peak forage availability. The latest neonate born to a post-treated female arrived 7.5 months after the peak in births from untreated females, indicating conception occurred within 24-31 days of the winter solstice. These results demonstrate surprising physiological plasticity for temperate latitude horses, and indicate that while photoperiod and temperature are powerful inputs driving the biological rhythms of conception and birth in horses, these inputs may not limit their ability to conceive under perturbed conditions. The protracted infertility observed in PZP-treated horses may be of benefit for managing overabundant wildlife, but also suggests caution for use in small refugia or rare species.
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Publication Date: 2013-01-28 PubMed ID: 23383018PubMed Central: PMC3557234DOI: 10.1371/journal.pone.0054972Google Scholar: Lookup
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  • Journal Article
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research investigates the effects of contraceptive use in feral horses, finding it can cause desynchronization between birth rates and available resources, which may threaten small populations’ viability.

Study Overview

  • The researchers followed three populations of feral horses in a longitudinal study. Their focus was on the effects of the immunocontraceptive porcine zona pellucida (PZP), specifically, how repeated vaccination extended infertility periods beyond the target.
  • They discovered that post-treatment fertility was lower in vaccinated horses, with only 25.6% giving birth compared to 64.1% of untreated females. These percentages pertain only to horses that had demonstrated fertility before the study.
  • Furthermore, the time required for parturition increased by 411.3 days for each consecutive year of treatment.

Impact of Contraception on Birth Timing

  • Under normal conditions, untreated horses’ births peaked in May, indicative of conception occurring around the previous summer solstice.
  • However, horses that had been treated and then conceived gave birth an estimated 31.5 days later than untreated females.
  • This shift resulted in a lack of alignment with peak forage availability. The extreme case saw a treated horse giving birth 7.5 months after the peak birth period in untreated horses—suggesting conception occurred close to the winter solstice.

Implications and Considerations

  • The results show a surprising flexibility in the horses’ reproductive systems, suggesting that factors like photoperiod and temperature do not limit conception under abnormal conditions created by human interference, such as PZP treatment.
  • The prolonged infertility observed in treated horses could be advantageous for controlling overpopulated species, but the researchers caution the use of such contraceptives for rare species or small populations, as the asynchrony between births and resource availability could threaten survival.

Cite This Article

APA
Ransom JI, Hobbs NT, Bruemmer J. (2013). Contraception can lead to trophic asynchrony between birth pulse and resources. PLoS One, 8(1), e54972. https://doi.org/10.1371/journal.pone.0054972

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 8
Issue: 1
Pages: e54972
PII: e54972

Researcher Affiliations

Ransom, Jason I
  • United States Geological Survey, Fort Collins Science Center, Fort Collins, CO, USA. Jason_I_Ransom@nps.gov
Hobbs, N Thompson
    Bruemmer, Jason

      MeSH Terms

      • Animals
      • Contraception / adverse effects
      • Female
      • Food Chain
      • Horses / physiology
      • Infertility, Female / physiopathology
      • Parturition / physiology
      • Parturition / radiation effects
      • Photoperiod
      • Probability
      • Seasons
      • Survival Analysis
      • Temperature

      Conflict of Interest Statement

      The authors have declared that no competing interests exist.

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