Maternal Size and Age Shape Offspring Size in a Live-Bearing Fish, Xiphophorus birchmanni

Abstract

Many studies of offspring size focus on differences in maternal investment that arise from ecological factors such as predation or competition. Classic theory predicts that these ecological factors will select for an optimal offspring size, and therefore that variation in a given environment will be minimized. Yet recent evidence suggests maternal traits such as size or age could also drive meaningful variation in offspring size. The generality of this pattern is unclear, as some studies suggest that it may represent non-adaptive variation or be an artifact of temporal or spatial differences in maternal environments. To clarify this pattern, we asked how maternal size, age and condition are related to each other in several populations of the swordtail Xiphophorus birchmanni. We then determined how these traits are related to offspring size, and whether they could resolve unexplained intra-population variation in this trait. We found that female size, age, and condition are correlated within populations; at some of these sites, older, larger females produce larger offspring than do younger females. The pattern was robust to differences among most, but not all, sites. Our results document a pattern that is consistent with recent theory predicting adaptive age- and size-dependence in maternal investment. Further work is needed to rule out non-adaptive explanations for this variation. Our results suggest that female size and age could play an under-appreciated role in population growth and evolution.

Heterogeneity in Individual Quality and Reproductive Trade-Offs Within Species

“…Additionally, we note that in some such organisms, such as Poeciliids, there can be between population variation in the strength of M‐O Size correlations (Kindsvater et al. ), offering a unique opportunity to study the ecological factors underlying reproductive correlations.…”

The relation between maternal phenotype and offspring size, explained by overhead material costs of reproduction

“…Larger females typically produce larger offspring (Fox and Czesak, 2000;Marshall and Keough, 2008;Kamler, 2005;Nasution et al, 2010;Rollinson and Hutchings, 2010;Sargent et al, 1987;Kindsvater et al, 2012), though there are exceptions to this rule and the relationship is sometimes weak (Fox and Czesak, 2000;Rollinson and Hutchings, 2010;Kindsvater et al, 2013). Much of the residual variation may be due to variation in maternal reserves, irrespective of variation in structural size.…”

“…SFM predicts that all offspring should have identical size, given by a single optimal value that does not depend on total reproductive effort (i.e., independent of E or n). However, the assumptions and predictions of SFM have been called into question, in light of observed variation in offspring size within and among females (Kaplan and Cooper, 1984;Reznick and Yang, 1993), correlations between egg size and total reproductive effort (Fox and Czesak, 2000;Caley et al, 2001;Beck and Beck, 2005;Nasution et al, 2010), and trends of increasing or decreasing offspring size with maternal size or age (Landa, 1992;Fox and Czesak, 2000;Kamler, 2005;Marshall and Keough, 2008;Kindsvater et al, 2012). In addition, offspring size and offspring number are two life history traits that must be investigated jointly, as they are tightly linked through the size-number tradeoff (Roff, 2002).…”

“…However, recent work (Marshall et al, 2010;Kindsvater et al, 2012) casts doubt on morphological constraints, as a general explanation for the relationship between maternal size and offspring size. Similarly, as also pointed out by Jørgensen et al (2011), explanations based on sib competition and other correlations between maternal phenotype and neonatal environment are taxon-specific (Hendry et al, 2001;Rollinson and Hutchings, 2010;Parker and Begon, 1986), and have proved to be problematic (Hendry and Day, 2003).…”

“…Similarly, as also pointed out by Jørgensen et al (2011), explanations based on sib competition and other correlations between maternal phenotype and neonatal environment are taxon-specific (Hendry et al, 2001;Rollinson and Hutchings, 2010;Parker and Begon, 1986), and have proved to be problematic (Hendry and Day, 2003). Given how common and taxonomically widespread the positive correlation between female and offspring sizes is (e.g., insects, Fox and Czesak, 2000;marine invertebrates, Marshall and Keough, 2008;Marshall et al, 2010;Nasution et al, 2010;fish, Reznick and Yang, 1993;Rollinson and Hutchings, 2010;Jørgensen et al, 2011;Kindsvater et al, 2012;plants, Sakai and Harada, 2001;, it is clear that some fundamental element is still missing from the picture.…”