Spatio-temporal variation in seed traits affects the occurrence and body-size pattern of a seed-feeding beetle (Chrysomelidae: Bruchinae) in Brazilian Cerrado

Abstract Seed quality is an important bottom-up factor driving life-history traits of seed beetles (Chrysomelidae: Bruchinae). However, information on how seed traits change spatiotemporally and affect herbivores' survival is incipient in Neotropics. We evaluated how the spatio-temporal variation in seed weight, hardness, size, and water content of Mimosa setosa var. paludosa (Fabaceae: Mimosoideae) affects the occurrence and body-size pattern of the seed beetle, Acanthoscelides quadridentatus (Schaeffer, 1907), in Brazilian Cerrado. We collected 400 fruits from four populations of M. setosa var. paludosa in Cerrado roadsides from Goias and Minas Gerais states and then we assessed in laboratory seed traits along with the weight and body size of A. quadridentatus. Additionally, we collected a total of 76 fruits (immature plus mature) in beginning and end of the fruiting phase and counted the frequencies of unhatched and hatched eggs of the seed beetle to evaluate the effect of seed hardening on beetle posture. We found greater seed damage in the population with softer, smaller and lighter seeds. Larger and heavier seeds were harder than smaller and lighter seeds; and male and female reared from larger and heavier seeds were respectively 15 and 25% larger than that reared from smaller and lighter seeds. We also found that weight and body size of A. quadridentatus were positively correlated with seed length, weight and water content. Unhatched eggs were found only in beginning of fruiting phase when seeds were immature and softer, suggesting the occurrence of a window of time in which females lay their eggs before seed hardening to facilitate the entry of first instar larvae. These results highlight that larger and heavier seeds are most protected against herbivory, but individuals of A. quadridentatus that overcome plant hardness can grow larger in size. We suggest that seed traits change across a spatio-temporal scale and affect life-history traits of A. quadridentatus.