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Individual mares bias investment in sons and daughters in relation to their condition.
Abstract: The Trivers-Willard hypothesis (TWH) predicts that a mother will treat a son or daughter differently depending on her ability to invest and the impact of her investment on offspring reproductive success. Although many studies have investigated the hypothesis, few have definitively supported or refuted it because of confounding factors or an inappropriate level of analysis. We studied maternal investment in sons and daughters in feral horses, Equus caballus, which meet the assumptions of the TWH with a minimum of confounding variables. Population level analyses revealed no differences in maternal behaviour towards sons and daughters. When we incorporated mare condition, we found that sons were more costly to mares in good condition, whereas daughters were more costly to mares in poor condition, although no differences in maternal behaviour were found. However, since the TWH makes predictions about individual mothers, we examined investment by mares who reared both a son and a daughter in different years of the study. Mares in good condition invested more in their sons in terms of maternal care patterns, costs to maternal body condition and costs to future reproduction. Conversely, mares in poor condition invested more in daughters. Therefore, with an appropriate level of analysis in a species in which confounding variables are minimal, the predictions of the Trivers-Willard hypothesis are supported. Copyright 2000 The Association for the Study of Animal Behaviour.
Publication Date: 2000-09-29 PubMed ID: 11007645DOI: 10.1006/anbe.2000.1480Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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This study explores how a mother horse’s health and wellbeing impacts her investment and behaviour towards either male or female offspring, ultimately supporting the Trivers-Willard hypothesis that a mother will treat offspring differently based on her capacity to care and the potential reproductive success of the offspring.
Background and Context
- The paper discussed is based on the Trivers-Willard hypothesis (TWH). This hypothesis states that a mother will alter her care and resources towards her offspring depending upon her health and condition, and how her care will impact the offspring’s reproductive success.
- This hypothesis, though widely known, has seldom been confirmed or debunked due to the presence of confounding factors or a lack of detailed data analysis.
- This study examines feral horses (Equus caballus) as their natural behaviors and characteristics make them ideal for testing the TWH with minimal confounding variables.
Research Findings
- Upon initial analysis, there was no discernible difference in how a mare treated male or female offspring. However, the situation changed when the mother’s health and conditions were taken into account.
- The study found that sons were more costly to mares in good health, whereas daughters were more costly to mares in poor health. However, it was noted that these cost differences didn’t alter the mare’s behavior towards the offspring.
- The breakthrough came when the study analyzed mares who gave offspring to both sons and daughters during different years. It was observed that mares in good condition invested more in their sons in terms of maternal care, cost to her own health, and future reproduction.
- In contrast, mares in poor condition were found to invest more in their daughters. This observation aligned with the TWH theory, affirming that a mother’s condition influences her resource distribution among offspring.
Conclusion
- The research distinctly highlights that the TWH can stand true in instances where confounding variables are kept to a bare minimum. The study brings clarity to how a mother’s condition can effectively influence how she nurtures and invests in her offspring.
- These findings deepen our understanding of maternal investment in animal species and the ever-complex relationships between mothers and their offspring within the natural world.
Cite This Article
APA
Cameron EZ, Linklater WL.
(2000).
Individual mares bias investment in sons and daughters in relation to their condition.
Anim Behav, 60(3), 359-367.
https://doi.org/10.1006/anbe.2000.1480 Publication
Researcher Affiliations
- Ecology Group, Institute of Natural Resources, Massey University
Citations
This article has been cited 16 times.- Medill SA, Janz DM, McLoughlin PD. Hair Cortisol Concentrations in Feral Horses and the Influence of Physiological and Social Factors. Animals (Basel) 2023 Jun 27;13(13).
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- Nuñez CMV, Rubenstein DI. Communication is key: Mother-offspring signaling can affect behavioral responses and offspring survival in feral horses (Equus caballus). PLoS One 2020;15(4):e0231343.
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- Sarkadi F, Szász E, Rosivall B. Socioeconomic status and sex ratio in the contemporary Hungarian population. Evol Hum Sci 2024;6:e38.
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