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Biological and environmental influences on parturition date and birth mass of a seasonal breeder.

Wolcott DM, Reitz RL, Weckerly FW - PLoS ONE (2015)

Bottom Line: Random effects revealed considerable variation among mothers and years.This study demonstrates that, in long-lived polytocous species, environmental factors may have a greater influence on natal features than previously supposed and the influence from biological factors is also complex.The documented responses to environmental influences provide unique insights into how mammalian seasonal reproductive dynamics may respond to current changes in climate.

View Article: PubMed Central - PubMed

Affiliation: Texas State University, Department of Biology, San Marcos, Texas, United States of America.

ABSTRACT
Natal features (e.g. Julian birth date and birth mass) often have fitness consequences and can be influenced by endogenous responses by the mother to seasonal fluctuations in nutritional quality and photoperiodic cues. We sought to further understand the biological and environmental factors that influence the natal features of a polytocous species in an environment with constant nutritional resources and limited seasonal variation. During a 36-year study we assessed the influence of biological factors (maternal age and litter type [i.e., litter size and sexual composition]) and environmental factors (total precipitation and mean maximum temperature during months encompassing conception, the last trimester of gestation, and the entire length of gestation) on Julian birth date and birth mass using linear-mixed effects models. Linear and quadratic functions of maternal age influenced both natal features with earliest Julian birth dates and heaviest birth masses occurring at prime-age and older individuals, which ranged from 5-9 years of age. Litter type influenced Julian birth date and birth mass. Interestingly, environmental factors affected Julian birth date and birth mass even though mothers were continuously allowed access to a high-quality diet. Random effects revealed considerable variation among mothers and years. This study demonstrates that, in long-lived polytocous species, environmental factors may have a greater influence on natal features than previously supposed and the influence from biological factors is also complex. The documented responses to environmental influences provide unique insights into how mammalian seasonal reproductive dynamics may respond to current changes in climate.

No MeSH data available.


Related in: MedlinePlus

Predicted values from a linear mixed effect model estimating the birth mass (kg) of captive white-tailed deer at Kerr Wildlife Management Area, Kerr County, Texas, USA from 1977–2012.Predicted birth mass was estimated across the range of each variable deemed important while controlling for all other variables (variable constants included: Maternal age = 4, Litter type = female singleton, Study program = study program 1, and December temperature = 16.0°C). The solid lines represent the predicted estimate for birth mass and the dashed lines are the standard error envelopes for the estimates. Random effects were treated as categorical variables and included a unique identifier for each mother and the year of birth for each fawn.
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pone.0124431.g004: Predicted values from a linear mixed effect model estimating the birth mass (kg) of captive white-tailed deer at Kerr Wildlife Management Area, Kerr County, Texas, USA from 1977–2012.Predicted birth mass was estimated across the range of each variable deemed important while controlling for all other variables (variable constants included: Maternal age = 4, Litter type = female singleton, Study program = study program 1, and December temperature = 16.0°C). The solid lines represent the predicted estimate for birth mass and the dashed lines are the standard error envelopes for the estimates. Random effects were treated as categorical variables and included a unique identifier for each mother and the year of birth for each fawn.

Mentions: Results for the birth mass analysis demonstrated that all biological factors influenced birth mass (Table 4). Inclusion of environmental factors, in the model selection analysis, suggested that December temperature explained the most variation in birth mass (Table 5). A summary of the selected model (Table 6) demonstrated that maternal age and precipitation each had a positive relationship on birth mass, with every 1 unit increase in maternal age and temperature (year, °C) increasing birth mass by 0.14 and 0.05 kg, respectively (Fig 4). The quadratic term for maternal age decreased birth mass as maternal age increased with the heaviest predicted birth masses (2.9 kg) occurring at 5 years of age (Fig 4). The post-hoc analysis assessing the possibility of a threshold or senescent effect after prime age revealed that linear and quadratic terms were not significant (F1,756 = 0.058, P = 0.810 and F1,756 = 0.058, P = 0.810, respectively), thus, there was a threshold effect. The lightest birth masses occurred at 2 years of age and heaviest at 5 years of age and older. Predicted values of birth mass for each litter type demonstrated that birth mass varied significantly among litter types. Females from mixed litter types had the lowest birth mass (FMix, 2.54 kg, SE = 0.04) followed by females of twin litters (F2, 2.61 kg, SE = 0.04), males of mixed litters (MMix, 2.68 kg, SE = 0.04), males of twin litters (M2, 2.70 kg, SE = 0.04), females of singleton litters (F1, 2.82 kg, SE = 0.04), and the heaviest birth masses were males of singleton litters (M1, 2.99 kg, SE = 0.04). Total birth mass for singleton and twin litters varied with total birth mass of singleton litters weighing less than twin litters (F1 = 2.82 kg, M1 = 2.99 kg, F2 = 5.22 kg, Mix = 5.22 kg, and M2 = 5.40 kg). Variance components for the random effects in the birth mass analysis were dam id (SD = 0.28), birth year (SD = 0.14), and residual error (SD = 0.41). The marginal R2 was 0.12 and the conditional R2 was 0.44. Inclusion of the random effects (dam id and birth year) along with the fixed effects explained more variation in birth mass than fixed effects alone.


Biological and environmental influences on parturition date and birth mass of a seasonal breeder.

Wolcott DM, Reitz RL, Weckerly FW - PLoS ONE (2015)

Predicted values from a linear mixed effect model estimating the birth mass (kg) of captive white-tailed deer at Kerr Wildlife Management Area, Kerr County, Texas, USA from 1977–2012.Predicted birth mass was estimated across the range of each variable deemed important while controlling for all other variables (variable constants included: Maternal age = 4, Litter type = female singleton, Study program = study program 1, and December temperature = 16.0°C). The solid lines represent the predicted estimate for birth mass and the dashed lines are the standard error envelopes for the estimates. Random effects were treated as categorical variables and included a unique identifier for each mother and the year of birth for each fawn.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401666&req=5

pone.0124431.g004: Predicted values from a linear mixed effect model estimating the birth mass (kg) of captive white-tailed deer at Kerr Wildlife Management Area, Kerr County, Texas, USA from 1977–2012.Predicted birth mass was estimated across the range of each variable deemed important while controlling for all other variables (variable constants included: Maternal age = 4, Litter type = female singleton, Study program = study program 1, and December temperature = 16.0°C). The solid lines represent the predicted estimate for birth mass and the dashed lines are the standard error envelopes for the estimates. Random effects were treated as categorical variables and included a unique identifier for each mother and the year of birth for each fawn.
Mentions: Results for the birth mass analysis demonstrated that all biological factors influenced birth mass (Table 4). Inclusion of environmental factors, in the model selection analysis, suggested that December temperature explained the most variation in birth mass (Table 5). A summary of the selected model (Table 6) demonstrated that maternal age and precipitation each had a positive relationship on birth mass, with every 1 unit increase in maternal age and temperature (year, °C) increasing birth mass by 0.14 and 0.05 kg, respectively (Fig 4). The quadratic term for maternal age decreased birth mass as maternal age increased with the heaviest predicted birth masses (2.9 kg) occurring at 5 years of age (Fig 4). The post-hoc analysis assessing the possibility of a threshold or senescent effect after prime age revealed that linear and quadratic terms were not significant (F1,756 = 0.058, P = 0.810 and F1,756 = 0.058, P = 0.810, respectively), thus, there was a threshold effect. The lightest birth masses occurred at 2 years of age and heaviest at 5 years of age and older. Predicted values of birth mass for each litter type demonstrated that birth mass varied significantly among litter types. Females from mixed litter types had the lowest birth mass (FMix, 2.54 kg, SE = 0.04) followed by females of twin litters (F2, 2.61 kg, SE = 0.04), males of mixed litters (MMix, 2.68 kg, SE = 0.04), males of twin litters (M2, 2.70 kg, SE = 0.04), females of singleton litters (F1, 2.82 kg, SE = 0.04), and the heaviest birth masses were males of singleton litters (M1, 2.99 kg, SE = 0.04). Total birth mass for singleton and twin litters varied with total birth mass of singleton litters weighing less than twin litters (F1 = 2.82 kg, M1 = 2.99 kg, F2 = 5.22 kg, Mix = 5.22 kg, and M2 = 5.40 kg). Variance components for the random effects in the birth mass analysis were dam id (SD = 0.28), birth year (SD = 0.14), and residual error (SD = 0.41). The marginal R2 was 0.12 and the conditional R2 was 0.44. Inclusion of the random effects (dam id and birth year) along with the fixed effects explained more variation in birth mass than fixed effects alone.

Bottom Line: Random effects revealed considerable variation among mothers and years.This study demonstrates that, in long-lived polytocous species, environmental factors may have a greater influence on natal features than previously supposed and the influence from biological factors is also complex.The documented responses to environmental influences provide unique insights into how mammalian seasonal reproductive dynamics may respond to current changes in climate.

View Article: PubMed Central - PubMed

Affiliation: Texas State University, Department of Biology, San Marcos, Texas, United States of America.

ABSTRACT
Natal features (e.g. Julian birth date and birth mass) often have fitness consequences and can be influenced by endogenous responses by the mother to seasonal fluctuations in nutritional quality and photoperiodic cues. We sought to further understand the biological and environmental factors that influence the natal features of a polytocous species in an environment with constant nutritional resources and limited seasonal variation. During a 36-year study we assessed the influence of biological factors (maternal age and litter type [i.e., litter size and sexual composition]) and environmental factors (total precipitation and mean maximum temperature during months encompassing conception, the last trimester of gestation, and the entire length of gestation) on Julian birth date and birth mass using linear-mixed effects models. Linear and quadratic functions of maternal age influenced both natal features with earliest Julian birth dates and heaviest birth masses occurring at prime-age and older individuals, which ranged from 5-9 years of age. Litter type influenced Julian birth date and birth mass. Interestingly, environmental factors affected Julian birth date and birth mass even though mothers were continuously allowed access to a high-quality diet. Random effects revealed considerable variation among mothers and years. This study demonstrates that, in long-lived polytocous species, environmental factors may have a greater influence on natal features than previously supposed and the influence from biological factors is also complex. The documented responses to environmental influences provide unique insights into how mammalian seasonal reproductive dynamics may respond to current changes in climate.

No MeSH data available.


Related in: MedlinePlus