Abstract
Female fitness is often influenced by trade-offs in energy allocated to reproduction or self-maintenance that is dependent upon the life history of the organism. Maternal body size and condition are factors that are often positively correlated with clutch size and offspring size. We investigated whether maternal body size (snout–vent length, SVL) and condition (residual of mass on SVL) could predict measures of reproductive success including clutch size, offspring body size (SVL), and offspring survival in the territorial Eastern Red-backed Salamander (Plethodon cinereus). Brooding females and their eggs were collected and then housed in a controlled laboratory setting. We recorded the number of eggs found with each female and separated offspring from females once hatched. At 40 d after hatching, we measured the SVL and mass of females and juveniles. Maternal SVL, but not condition, was positively related to clutch size and offspring SVL; however, there was no significant relationship between clutch size and offspring SVL, indicating no trade-off between number and body size of offspring. In the laboratory, survival of the offspring to 185 d post-hatching was positively related to maternal SVL and negatively related to maternal condition. Also, the mean SVL, measured on day 40, of the offspring that survived to 185 d was significantly greater than the SVL of the offspring that did not survive, indicating a benefit of larger offspring body size. Finally, subsequent egg production (number of new oocytes produced by females following the current reproductive bout) was positively related to maternal SVL and condition (measured 185 d after hatching their previous clutches). These results suggest that larger maternal body size and condition of Eastern Red-backed Salamanders provide increased reproductive success through the number and body size of offspring produced in current or subsequent reproductive bouts and in offspring survival. Large body size in territorial animals like P. cinereus provides benefits for holding high quality territories as well as for increased reproductive success.
Highlights
D IFFERENTIAL acquisition of limited resources for reproduction will occur when some individuals in a population have a competitive advantage over others and are able to sequester a larger proportion of those resources. Brockelman (1975) modeled the expected fitness of parents relative to territorial quality, predicting that in territorial species, selection for greater parental investment per offspring should occur
Clutch size was positively correlated with maternal snout–vent length (SVL) (Fig. 1A)
In a separate multiple regression analysis, we found that maternal body size and condition did not predict hatch date, defined as the date juveniles began to emerge from the eggs (R2adj 1⁄4 0.004; F2,49 1⁄4 1.102; P 1⁄4 0.340)
Summary
D IFFERENTIAL acquisition of limited resources for reproduction will occur when some individuals in a population have a competitive advantage over others and are able to sequester a larger proportion of those resources (e.g., in territorial species). Brockelman (1975) modeled the expected fitness of parents relative to territorial quality, predicting that in territorial species, selection for greater parental investment per offspring should occur. We tested the hypothesis that maternal body size and condition affect measures of reproductive success (defined as a female’s production of offspring in a single reproductive bout) including clutch size, offspring body size, and offspring survival using a well-studied population of the territorial Eastern Red-backed Salamander, Plethodon cinereus This species is completely terrestrial, inhabiting temperate forests of northeastern North America. The neonates remain near their mothers for up to three months (Gillette, 2003) This brooding period can be costly because brooding females do not forage for prey and lose a significant amount of mass that results in insufficient reserves to produce a clutch in the year (Ng and Wilbur, 1995; Yurewicz and Wilbur, 2004), and females in better condition (e.g., more mass for a given body length or having intact tails) produce more and larger maturing oocytes than females in worse condition (Fraser, 1980; Yurewicz and Wilbur, 2004; Evans et al, 2020). In a cross-fostering experiment, Crespi and Lessig (2004) found that brooding foster-females of P. cinereus with larger body sizes produced larger hatchlings than did smaller foster-females, regardless of the body size of the genetic mother from which the eggs originated
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