Geometry for the selfish clutch? Protective geometry and reproductive anatomy as candidate determinants of clutch size variation in pentatomid bugs

Authors: ABRAM, PAUL - Agriculture And Agri-Food Canada; GUERRA-GRENIER, ERIC - McGill University - Canada; BRODEUR, JACQUES - Quebec Research Fund; CAPKO, CLARISSA, CAPKO, CLARISSA - University Of Fraser Valley; BEERS, ELIZABETH - Washington State University; BLASSIOLI, CAROLINA - Embrapa Genetic Resources; BORGES, MIGUEL - Embrapa Genetic Resources; CINGOLANI, FERNANDA - Center For Studies Of Parasites And Vectors, Cepave; CUSUMANO, ANTONINO - University Of Palermo Italy; DE CLERCQ, PATRICK - Ghent University; FERNANDEZ, CELINA - Centro De Referencía De Micologia (CEREMIC) Facultad De Ciencias Bioquímicas Y Farmacéuticas, Unive; GARIEPY, TARA - Agriculture And Agri-Food Canada; HAYE, TIM - Commonwealth Agricultural Bureau International (CABI) - Switzerland; Hoelmer, Kim; LAUMANN, RAUL - Embrapa; LIETTI, MARCELA - Centro De Referencía De Micologia (CEREMIC) Facultad De Ciencias Bioquímicas Y Farmacéuticas, Unive; MCPHERSON, J.E. - Southern Illinois University; PUNSCKE, EDUARDO - Centro De Referencía De Micologia (CEREMIC) Facultad De Ciencias Bioquímicas Y Farmacéuticas, Unive; SAUNDERS, TOM - University Of Auckland; ZHANG, JIN PING - Institute Of Plant Protection - China; HARDY, IAN C.W. - University Of Helsinki

Submitted to: The American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2022
Publication Date: 5/24/2023
Citation: Abram, P.K., Guerra-Grenier, E., Brodeur, J., Capko, Clarissa, C., Beers, E., Blassioli, C., Borges, M., Cingolani, F.M., Cusumano, A., De Clercq, P., Fernandez, C.A., Gariepy, T.D., Haye, T., Hoelmer, K.A., Laumann, R., Lietti, M., McPherson, J., Punscke, E., Saunders, T., Zhang, J., Hardy, I. 2023. Geometry for the selfish clutch? Protective geometry and reproductive anatomy as candidate determinants of clutch size variation in pentatomid bugs. The American Naturalist. https://doi.org/10.1086/725917.
DOI: https://doi.org/10.1086/725917

Interpretive Summary: Some insects lay their eggs in clusters, and eggs at edges of these clusters are more exposed to attack by natural enemies. This study examined data from 48 species of pentatomid stink bugs, a group that includes many crop pests and predatory species. Stink bugs tend to lay egg masses in shapes that protect more of their offspring as numbers of eggs per cluster increase. However, the most common clutch sizes of either 14 or 28 eggs are related to the number of ovarioles in female ovaries, indicating that reproductive anatomy is more important in these species than setting clutch size than the geometry of the egg mass. In other species, clutch size is unrelated to ovary structure. These findings will help to inform further research on the ecology and biological control of stink bug pests.

Technical Abstract: Some animals lay their eggs in clusters, and eggs on the periphery of these clusters can be at higher risk of mortality; for instance, due to desiccation or attack by natural enemies. Using a data set from 48 species of pentatomid stink bugs, we asked whether the most commonly occurring clutch sizes could result from geometrical arrangements that maximize the proportion of eggs in the egg mass interior. We found that, while the most common clutch sizes do not correspond with geometric optimality, stink bugs do tend to lay egg masses in shapes that protect increasing proportions of their offspring as clutch sizes increase. We also considered whether ovariole number, an aspect of reproductive anatomy that may be a fixed trait across many pentatomids, could explain observed distributions of clutch sizes. The most common clutch sizes across many species correspond with multiples of ovariole number, with many species with seven ovarioles usually laying either 14 or 28 eggs per clutch. There are species with the same number of ovarioles that, however, lay clutches of widely varying size, among which multiples of ovariole number are not over-represented. Our results indicate that stink bug reproductive anatomy is a more important determinant of clutch size uniformity than is clutch geometry. However, laying larger clutch sizes may impose selection for increasingly protective geometry. These findings also highlight how variability in reproductive structures is not prerequisite for diversity in reproductive strategies. Rather, within a group of animals that has lost most of its variation in ovariole number, clutches with a broad range of characteristics (uniformity, size, shape, clustering) may still be laid.