Author's personal copy Mating rate influences female reproductive investment in a simultaneous hermaphrodite, Lymnaea stagnalis

Multiple mating often imposes direct fitness costs on females but can provide indirect benefits such as enhanced genetic diversity and offspring quality. The costs and benefits of multiple mating have been investigated extensively in separate-sex species but less so in simultaneous hermaphrodites, despite being highly relevant given their flexible resource allocation and ability to compensate for costs experienced in one sexual role by gains in the opposite role. At high mating rates, the promiscuous hermaphroditic pond snail Lymnaea stagnalis experiences depressed female fecundity mediated by seminal fluid compounds. By experimentally manipulating mating opportunities, we tested for effects on female reproductive investment over 10 weeks. As expected, continuous access to mating partners resulted in decreased female investment, in terms of both total number of eggs (fecundity) and egg mass dry weight. Total investment in offspring increased over time for all treatments but was significantly less pronounced in treatments with continuous access to partners, and this was irrespective of partner identity. Investment per offspring was positively correlated with higher mating rates across treatments. Thus, multiple mating resulted in higher investment in egg masses at low than at higher mating rates. In contrast, at higher mating rates the investment per egg was higher. We conclude that, in L. stagnalis, mating multiply can severely impact female reproductive success and, although we cannot entirely exclude reallocation of resources to the male function from this study, we argue that this is probably the result of sexual conflict caused by previously identified seminal fluid components.

Stability and Function of Hippocampal Mossy Fiber Synapses Depend on Bcl11b/Ctip2

Structural and functional plasticity of synapses are critical neuronal mechanisms underlying learning and memory. While activity-dependent regulation of synaptic strength has been extensively studied, much less is known about the transcriptional control of synapse maintenance and plasticity. Hippocampal mossy fiber (MF) synapses connect dentate granule cells to CA3 pyramidal neurons and are important for spatial memory formation and consolidation. The transcription factor Bcl11b/Ctip2 is expressed in dentate granule cells and required for postnatal hippocampal development. Ablation of Bcl11b/Ctip2 in the adult hippocampus results in impaired adult neurogenesis and spatial memory. The molecular mechanisms underlying the behavioral impairment remained unclear. Here we show that selective deletion of Bcl11b/Ctip2 in the adult mouse hippocampus leads to a rapid loss of excitatory synapses in CA3 as well as reduced ultrastructural complexity of remaining mossy fiber boutons (MFBs). Moreover, a dramatic decline of long-term potentiation (LTP) of the dentate gyrus-CA3 (DG-CA3) projection is caused by adult loss of Bcl11b/Ctip2. Differential transcriptomics revealed the deregulation of genes associated with synaptic transmission in mutants. Together, our data suggest Bcl11b/Ctip2 to regulate maintenance and function of MF synapses in the adult hippocampus

Image_1.TIF

<p>Structural and functional plasticity of synapses are critical neuronal mechanisms underlying learning and memory. While activity-dependent regulation of synaptic strength has been extensively studied, much less is known about the transcriptional control of synapse maintenance and plasticity. Hippocampal mossy fiber (MF) synapses connect dentate granule cells to CA3 pyramidal neurons and are important for spatial memory formation and consolidation. The transcription factor Bcl11b/Ctip2 is expressed in dentate granule cells and required for postnatal hippocampal development. Ablation of Bcl11b/Ctip2 in the adult hippocampus results in impaired adult neurogenesis and spatial memory. The molecular mechanisms underlying the behavioral impairment remained unclear. Here we show that selective deletion of Bcl11b/Ctip2 in the adult mouse hippocampus leads to a rapid loss of excitatory synapses in CA3 as well as reduced ultrastructural complexity of remaining mossy fiber boutons (MFBs). Moreover, a dramatic decline of long-term potentiation (LTP) of the dentate gyrus-CA3 (DG-CA3) projection is caused by adult loss of Bcl11b/Ctip2. Differential transcriptomics revealed the deregulation of genes associated with synaptic transmission in mutants. Together, our data suggest Bcl11b/Ctip2 to regulate maintenance and function of MF synapses in the adult hippocampus.</p