Increased copulation duration does not necessarily reflect a proportional increase in the number of transferred spermatozoa

Post-copulatory sexual selection research tends to focus on the numerous adaptations that have evolved to increase the chances of donated spermatozoa fertilizing oocytes. Even though fertilization obviously directly depends on the presence of sufficient, viable spermatozoa, the quantification of the sperm transfer process itself has not received the attention it deserves. Here, we present experimental work on a simultaneously hermaphroditic snail in combination with a review of the literature focussing on the relationship between the duration of copulation and the number of sperm that are transferred. Based on classical work, this relationship is often assumed to be linear, but as we show here this need not be the case. Both our experimental data and the reviewed literature indicate that there are clear instances where the process of sperm transfer is not a linear process, i.e., longer copulation duration does not necessarily imply more transfer of sperm. As we point out, there seems to be a bias in the literature towards investigating this in insects, but other animal groups in which this has been investigated do show similar relationships. To conclude, we discuss how the specific patterns of sperm transfer that have been reported can be biologically interpreted and we caution that simply using copulation duration as a proxy for the number of sperm transferred can be misleading

Comparative toxicity of imidacloprid and thiacloprid to different species of soil invertebrates

Neonicotinoid insecticides have come under increasing scrutiny for their impact on non-target organisms, especially pollinators. The current scientific literature is mainly focused on the impact of these insecticides on pollinators and some aquatic insects, leaving a knowledge gap concerning soil invertebrates. This study aimed at filling this gap, by determining the toxicity of imidacloprid and thiacloprid to five species of soil invertebrates: earthworms (Eisenia andrei), enchytraeids (Enchytraeus crypticus), Collembola (Folsomia candida), oribatid mites (Oppia nitens) and isopods (Porcellio scaber). Tests focused on survival and reproduction or growth, after 3–5 weeks exposure in natural LUFA 2.2 standard soil. Imidacloprid was more toxic than thiacloprid for all species tested. F. candida and E. andrei were the most sensitive species, with LC50s of 0.20–0.62 and 0.77 mg/kg dry soil for imidacloprid and 2.7–3.9 and 7.1 mg/kg dry soil for thiacloprid. EC50s for effects on the reproduction of F. candida and E. andrei were 0.097–0.30 and 0.39 mg/kg dry soil for imidacloprid and 1.7–2.4 and 0.44 mg/kg dry soil for thiacloprid. The least sensitive species were O. nitens and P. scaber. Enchytraeids were a factor of 5–40 less sensitive than the taxonomically related earthworm, depending on the endpoint considered. Although not all the species showed high sensitivity to the neonicotinoids tested, these results raise awareness about the effects these insecticides can have on non-target soil invertebrates