Biology subjects

Bressac, C.

Publications and source records attributed to Bressac, C..

3 recordsLinked to original sources

bioRxiv2024

Gone but not forgotten: dynamics of sperm storage and potential ejaculate digestion in the black soldier fly Hermetia illucens

When it comes to describe reproduction in internally fertilized species, understanding the dynamics of sperm storage is crucial to unravel the complexity of post-copulatory sexual selection processes. This physiological process goes from sperm transfer to its use for fertilization. In this framework, the spatiotemporal dynamics of sperm storage were described in the black soldier fly (BSF) with fluorescence and transmission electron microscopy (TEM). Besides being of great economic interest, BSF females have highly compartmentalized spermathecae. Spermatozoa were counted both during and after mating in two successive spermathecae compartments: the fishnet canals and the reservoirs. In addition to seminal fluids, male transfers a sperm plug in the fishnet canals, then only some spermatozoa reach the reservoirs over 2 days. TEM observations of the fishnet canals revealed potential digestive functions, explaining the decline in the number and the viability of spermatozoa that have not been stored in the reservoirs. After one mating, females laid up to three fertile clutches, evidencing no constraints on sperm quantity or quality. Spermatic and ultrastructural investigations strongly suggest that BSF ejaculate acts both as a sperm plug and a as nuptial gift, reinforcing the interest in studying this insect as a model for sexual selection.

evolutionary biology↗

bioRxiv2023

Sperm production and allocation respond to perceived risk of sperm competition in the black soldier fly Hermetia illucens

In polyandrous species, competition between males for offspring paternity goes on after copulation through the competition of their ejaculates for the fertilisation of females oocytes. Given that males allocating more spermatozoa are favored, different models of sperm competition predict adaptive plasticity in male sperm production and allocation. These predictions were tested experimentally in the black soldier fly (BSF) Hermetia illucens. In this farmed insect, adult biology is little known despite the economic interest of larvae for bioconversion and as an animal feedstuff. Two sets of experiments were carried out to modify the risk of sperm competition perceived by males. The first consisted of placing adult males alone or in groups of 10 - modifying mean risk of sperm competition - and then measuring their sperm production. The second took place at the beginning of copulation; pairs with males from the two mean risk of sperm competition treatments were transferred to different contexts of immediate risk of sperm competition (empty cages, cages containing 10 males, or cages containing 10 females) and the number of spermatozoa stored by the females was counted. Males reared in groups of 10 showed more spermatozoa in their seminal vesicles than males reared alone. Regarding sperm allocation, females that mated in the presence of conspecifics - either 10 males or 10 females - stored more spermatozoa than those that mated alone. This study shows that sperm production and allocation are dependent on sperm competition risk in BSF, revealing a plasticity of reproduction under socio-sexual situations.

evolutionary biology↗

bioRxiv2020

Chromosomal resolution reveals symbiotic virus colonization of parasitic wasp genomes

Most endogenous viruses, an important proportion of eukaryote genomes, are doomed to slowly decay. Little is known, however, on how they evolve when they confer a benefit to their host. Bracoviruses are essential for the parasitism success of parasitoid wasps, whose genomes they integrated ~103 million years ago. Here we show, from the assembly of a parasitoid wasp genome, for the first time at a chromosomal scale, that symbiotic bracovirus genes spread to and colonized all the chromosomes. Moreover, large viral clusters are stably maintained suggesting strong evolutionary constraints. Genomic comparison with another wasps revealed that this organization was already established ~53 mya. Transcriptomic analyses highlight temporal synchronization of viral gene expression, leading to particle production. Immune genes are not induced, however, indicating the virus is not perceived as foreign by the wasp. This recognition suggests that no conflicts remain between symbiotic partners when benefits to them converge.

genomics↗