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1. Changes in stable isotope compositions during fasting in phocid seals

   https://doi.org/10.1002/rcm.8308  

   Habran, Sarah ; Damseaux, France ; Pomeroy, Paddy ; Debier, Cathy ; Crocker, Daniel ; Lepoint, Gilles ; Das, Krishna ( December 2018 , Rapid Communications in Mass Spectrometry)

   The grey seal,Halichoerus grypus(GS), and the northern elephant seal,Mirounga angustirostris(NES), come ashore for reproduction. This period involves intense physiological processes such as lactation in females and a developmental post‐weaning fast in juveniles. Previous studies have shown thatδ¹³C andδ¹⁵N values are affected by starvation, but the precise effects of fasting associated with lactation and post‐weaning fast in seals remain poorly understood.

   To examine the effect of lactation and post‐weaning fast on stable isotope ratios in GS and NES, blood and hair were sampled from 21 GS mother‐pup pairs on the Isle of May and on 22 weaned NES pups at Año Nuevo State Reserve during their respective breeding seasons. Milk samples were also collected from GS mothers. Stable isotope measurements were performed with an isotope ratio mass spectrometer coupled to an N‐C elemental analyser.

   Changes in stable isotope ratios in blood components during fasting were similar and weak between GS and NES mothers especially in blood cells (GS:Δ¹⁵N = 0.05‰,Δ¹³C = 0.02‰; NES:Δ¹⁵N = 0.1‰,Δ¹³C = 0.1‰). GS showed a¹⁵N discrimination factor between maternal and pup blood cells and milk, but not for¹³C. The strongest relationship between the isotopic compositions of the mother and the pup was observed in the blood cells.

   Isotopic consequences of lactation, fasting, and growth seem limited in NES and GS, especially in medium‐term integrator tissues of feeding activity such as blood cells. Stable isotope ratios in the blood of pups and mothers are correlated. We observed a subtle mother‐to‐pup fractionation factor. Our results suggest that pup blood cells are mostly relevant for exploring the ecology of female seals.

    

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2. Birth dates vary with fixed and dynamic maternal features, offspring sex, and extreme climatic events in a high‐latitude marine mammal

   https://doi.org/10.1002/ece3.1985  

   Rotella, Jay J. ; Paterson, J. Terrill ; Garrott, Robert A. ( February 2016 , Ecology and Evolution)

   Reproductive synchrony tends to be widespread in diverse species of plants and animals, especially at higher latitudes. However, for long‐lived mammals, birth dates for different individuals can vary by weeks within a population. A mother's birth timing can reveal useful information about her reproductive abilities and have important implications for the characteristics and survival of her offspring. Despite this, our current knowledge of factors associated with variation in birth dates is modest. We used long‐term data for known‐age Weddell seals in Antarctica and a Bayesian hierarchical modeling approach to study how birth dates varied with fixed and temporally varying features of mothers, whether sex allocation varied with birth timing, and annual variation in birth dates. Based on birth dates for 4465 pups born to 1117 mothers aged 4–31, we found that diverse features of mothers were associated with variation in birth dates. Maternal identity was the most important among these. Unlike most studies, which have reported that birth dates occur earlier as mothers age, we found that birth dates progressively occurred earlier in the year in the early part of a mother's reproductive life, reached a minimum at age 16, and then occurred later at later ages. Birth dates were positively related to a mother's age at primiparity and recent reproductive effort. The earliest birth dates were for pups born to prime‐age mothers who did not reproduce in the previous year but began reproduction early in life, suggesting that females in the best condition gave birth earlier than others. If so, our finding that male pups tended to be born earlier than females provides support for the Trivers–Willard sex‐allocation model. Average birth dates were quite consistent across years, except for 2 years that had notable delays and occurred during the period when massive icebergs were present and disrupted the ecosystem.

    

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3. Maternal size and body condition predict the amount of post‐fertilization maternal provisioning in matrotrophic fish

   https://doi.org/10.1002/ece3.4542  

   Hagmayer, Andres ; Furness, Andrew I. ; Reznick, David N. ; Pollux, Bart J. A. ( December 2018 , Ecology and Evolution)

   Maternal effects often provide a mechanism for adaptive transgenerational phenotypic plasticity. The maternal phenotype can profoundly influence the potential for such environmentally induced adjustments of the offspring phenotype, causing correlations between offspring and maternal traits. Here, we study potential effects of the maternal phenotype on offspring provisioning prior to and during gestation in the matrotrophic live‐bearing fish speciesPoeciliopsis retropinna. Specifically, we examine how maternal traits such as body fat, lean mass, and length relate to pre‐ (i.e., allocation to the egg prior to fertilization) and post‐fertilization (i.e., allocation to the embryo during pregnancy) maternal provisioning and how this ultimately affects offspring size and body composition at birth. We show that pre‐ and post‐fertilization maternal provisioning is associated with maternal length and body fat, but not with maternal lean mass. Maternal length is proportionally associated with egg mass at fertilization and offspring mass at birth, notably without changing the ratio of pre‐ to post‐fertilization maternal provisioning. This ratio, referred to as the matrotrophy index (MI), is often used to quantify the level of matrotrophy. By contrast, the proportion of maternal body fat is positively associated with post‐fertilization, but not pre‐fertilization, maternal provisioning and consequently is strongly positively correlated with the MI. We furthermore found that the composition of embryos changes throughout pregnancy. Females invest first in embryo lean mass, and then allocate fat reserves to embryos very late in pregnancy. We argue that this delay in fat allocation may be adaptive, because it delays an unnecessary high reproductive burden to the mother during earlier stages of pregnancy, potentially leading to a more slender body shape and improved locomotor performance. In conclusion, our study suggests that (a) offspring size at birth is a plastic trait that is predicted by both maternal length and body fat, and (b) the MI is a plastic trait that is predicted solely by the proportion of maternal body fat. It herewith provides new insights into the potential maternal causes and consequences of embryo provisioning during pregnancy in matrotrophic live‐bearing species.

    

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4. Investigating diverse sources of variation in the amount of time Weddell seal ( Leptonychotes weddellii ) pups spend in the water during the lactation period

   https://doi.org/10.1111/mms.12955  

   Petch, Shane M. ; Rotella, Jay J. ; Link, William A. ; Paterson, J. Terrill ; Garrott, Robert A. ( July 2022 , Marine Mammal Science)

   Field observations suggest that time spent in the water by Weddell seal pups during lactation varies among individuals, which could yield important developmental tradeoffs. We analyzed data from 713 pups born to 419 different mothers over 9 years to evaluate total time in the water, age at first entry, and potential sources of variation using temperature loggers attached to the rear flipper of pups. Pups first entered the water at 11–29 days of age (M = 14.9) and spent 4–204 hr (M = 69.3) in the water by 30 days of age. Age at first entry was earlier for pups with higher birth mass and mothers of above average reproductive experience. Total time in the water was related to maternal identity and greater for female pups and for pups that had higher birth mass, mothers of intermediate age, mothers that skipped reproduction in the previous year, and for pups that first entered the water at younger ages. Phenotypic traits explain observed variation in the development of a key life history behavior in the Weddell seal. Strong individual variation in time spent in metabolically costly swimming and diving might lead to variation in growth, energy stores, and survival and fitness outcomes.

    

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5. Meager Milk: Lasting Consequences for Adult Daughters of Primiparous Mothers Among Rhesus Macaques ( Macaca mulatta )

   https://doi.org/10.1093/icb/icad022  

   Pittet, Florent ; Hinde, Katie ( May 2023 , Integrative And Comparative Biology)

   Among mammals, primipara who initiate reproduction before full maturity can be constrained in their maternal investment, both due to fewer somatic resources and tradeoffs between their own continued development and reproductive effort. Primipara are particularly limited in their capacity to synthesize milk during lactation, the costliest aspect of reproduction for most mammals, especially primates due to long periods of postnatal development. Due to reduced milk transfer, Firstborns may be at elevated risk for long-term consequences of deficits in early life endowment from their primiparous mothers. Here we investigated mass, growth, stature, and lactation performance among N = 273 adult daughters across N = 335 reproductions, who were their own mother’s Firstborn or Laterborn progeny, among rhesus macaques (Macaca mulatta) at the California National Primate Research Center. We further explored mass during infancy of the offspring of Firstborn and Laterborn mothers. Firstborns had accelerated growth during infancy, but had slowed growth during juvenility, compared to Laterborns. Although both Firstborns and Laterborns were the same age at reproductive debut, Firstborns had lower body mass, an effect that persisted throughout the reproductive career. Available milk energy, the product of milk energetic density and milk yield, was on average 16% lower for Firstborns compared to Laterborns, a difference that was only partially mediated by their lower mass. Despite differences in their mothers’ energy provision through milk, the mass of infants of Firstborn and Laterborn mothers did not differ at peak lactation, suggesting that infants of Firstborns devote a higher proportion of milk energy to growth than infants of Laterborns. To date few studies have explored how early life conditions shape capacities to synthesize milk and milk composition. Our findings contribute new information among primates on how early life maternal endowments are associated with persistent effects long after the period of maternal dependence well into reproductive maturity.

    

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