Resource-dependent investment in male sexual traits in a viviparous fish

Abstract

Exaggerated and conspicuous sexually selected traits are often costly to produce and maintain. Costly traits are expected to show resource-dependent expression, since limited resources prevent animals from investing maximally in multiple traits simultaneously. However, there may be critical periods during an individual’s life where the expression of traits is altered if resources are limited. Moreover, costly sexual traits may arise from sexual selection acting both before (pre-copulatory) and after mating (post-copulatory). Gaining a robust understanding of resource-dependent trait expression therefore requires an approach that examines both episodes of sexual selection after resource limitation during different times in an individual’s life. Yet few studies have taken such an approach. Here, we examine how resource restriction influences a set of pre- and post-copulatory traits in male pygmy halfbeaks (Dermogenys collettei), which invest in sexual ornaments and routinely engage in male–male contests and sperm competition. Critically, we examined responses in males when resources were restricted during development and after reaching sexual maturity. Both pre- and post-copulatory traits are resource-dependent in male halfbeaks. Body size, beak size, courtship behavior, and testes size were reduced by diet restriction, while, unexpectedly, the restricted-diet group had a larger area of red color on the beak and fins after diet treatment. These patterns were generally consistent when resources were restricted during development and after reaching sexual maturity. The study reinforces the role of resource acquisition in maintaining variation among sexual traits.

Examining the potential for resource‐dependent female reproductive fluid‐sperm interactive effects in a livebearing fish

“…Pairs of size matched females (to ensure no size‐difference prior to diet treatments) were randomly assigned to either a high or restricted diet treatment group. Females were fed different amounts of fruit flies ( D. melanogaster ) throughout the diet treatment (sensu Fernlund Isaksson et al, 2022). Females assigned to the high‐diet treatment were fed 36 fruit flies/week (6 flies/day, 6 days/week), while females assigned to the restricted diet treatment were fed 9 fruit flies/week (1 fly/day on 3 days and 2 flies/day on 3 days each week).…”

“…Traditionally, sexual selection research has focused on resource dependent expression of pre‐copulatory traits in males, focusing on courtship or competition behaviours and ornaments (Cotton et al, 2004). More recently, research effort has examined resource‐dependence of ejaculate traits involved in post‐copulatory sexual selection (Fernlund Isaksson et al, 2022; Macartney et al, 2019). However, limited resources can also influence how sexual selection operates in females.…”

“…Halfbeaks live in mixed‐sex shoals and readily interact in intersexual behaviours of courtship and competition (Devigili et al, 2021; Greven, 2010). Female halfbeaks mate multiply and can store sperm for several months (Greven, 2010; EFI personal observation) suggesting that post‐copulatory sexual selection in males is strong (Devigili et al, 2021; Fernlund Isaksson et al, 2022). A recent study revealed resource‐dependency of post‐copulatory investment in male halfbeaks (Fernlund Isaksson et al, 2022).…”

“…Female halfbeaks mate multiply and can store sperm for several months (Greven, 2010; EFI personal observation) suggesting that post‐copulatory sexual selection in males is strong (Devigili et al, 2021; Fernlund Isaksson et al, 2022). A recent study revealed resource‐dependency of post‐copulatory investment in male halfbeaks (Fernlund Isaksson et al, 2022). In particular, male halfbeaks maintained on restricted diets had shorter beaks (elongated lower jaws), invested less in testicular tissue, and performed less courtship towards females, while sperm viability, swimming velocity and morphology were unaffected by resource restriction (Fernlund Isaksson et al, 2022).…”

“…A recent study revealed resource-dependency of post-copulatory investment in male halfbeaks (Fernlund Isaksson et al, 2022). In particular, male halfbeaks maintained on restricted diets had shorter beaks (elongated lower jaws), invested less in testicular tissue, and performed less courtship towards females, while sperm viability, swimming velocity and morphology were unaffected by resource restriction (Fernlund Isaksson et al, 2022). However, it is not known whether resource restriction influences reproductive traits in female halfbeaks.…”