Sperm design and variation in the New World blackbirds (Icteridae)

Post-copulatory sexual selection (PCSS) is thought to be one of the evolutionary forces responsible for the rapid and divergent evolution of sperm design. However, whereas in some taxa particular sperm traits are positively associated with PCSS, in other taxa, these relationships are negative, and the causes of these different patterns across taxa are poorly understood. In a comparative study using New World blackbirds (Icteridae), we tested whether sperm design was influenced by the level of PCSS and found significant positive associations with the level of PCSS for all sperm components but head length. Additionally, whereas the absolute length of sperm components increased, their variation declined with the intensity of PCSS, indicating stabilizing selection around an optimal sperm design. Given the diversity of, and strong selection on, sperm design, it seems likely that sperm phenotype may influence sperm velocity within species. However, in contrast to other recent studies of passerine birds, but consistent with several other studies, we found no significant link between sperm design and velocity, using four different species that vary both in sperm design and PCSS. Potential reasons for this discrepancy between studies are discussed

Effects of soil type and adult size on mating propensity and reproductive output in two populations of the land snail Arianta arbustorum (Linnaeus)

Life-history traits in terrestrial gastropods may be influenced by both abiotic and biotic factors. This study examines the effects of soil type and adult size (shell volume) on mating propensity and female and male reproductive output (number and mass of eggs, number of sperm delivered and spermatophore mass) in individuals of the simultaneous hermaphrodite land snail Arianta arbustorum from two populations kept both on calcium-(Ca-)rich and Ca-poor soil. Snails from the two populations differed in adult size, relative shell growth, mating propensity and egg size. Furthermore, in both populations the number of egg batches deposited, egg size and spermatophore size scaled allometrically with shell volume, but not the total number of eggs produced and number of sperm delivered. Independent of population and shell size, the type of soil on which the snails were maintained influenced mating propensity, the total number of eggs produced and the mass of the albumen gland (another measure of female reproductive output). The mating propensity was higher and the total number of eggs produced was larger in snails kept on Ca-poor soil than in individuals reared on Ca-rich soil. This surprising finding could be explained by the fact that the Ca-poor soil used in the experiment still contained enough Ca to allow reproduction, and that the snails ingested Ca through the food consumed (lettuce grown on Ca-rich soil was available ad libitum). Moreover, the Ca-rich soil could contain minerals or (unknown) substances which discourage reproduction in A. arbustorum. Our study highlights the complexities faced when interpreting differences in the life history of gastropods. Explaining interpopulational differences in life-history patterns requires not only the understanding of the influence of snail origin, but also an understanding of the effects of shell size, substratum type (soil type), food and local climate

Elevated plasma N-terminal ProBNP levels in unmedicated patients with major depressive disorder

There is considerable evidence that cardiovascular diseases are more prevalent in patients with major depressive disorder (MDD). Secretion of N-terminal pro-B-type natriuretic peptide (NT-proBNP) increases in several cardiac illnesses, making this neurohormone a reliable diagnostic and prognostic biomarker of cardiovascular risk. We measured plasma NT-proBNP levels in the following three groups of subjects free of overt cardiovascular disease: unmedicated patients with MDD (n=40), unmedicated patients with schizophrenia (n=44), and normal control subjects (n=42). The severity of depressive symptoms was rated using the Hamilton Depression Rating Scale (HAMD). Plasma NT-proBNP levels were assayed by ELISA. Plasma NT-proBNP levels were significantly higher in the MDD group (median: 217.1 pmol/L; interquartile range: 179.4-277.1 pmol/L) than in patients with schizophrenia (175.7 pmol/L [139.0-218.9]; P<0.05) or in the control group (158.9 pmol/L [98.3-212.1]; P<0.001). Among patients with MDD, there was a significant positive correlation (Spearman's rank correlation=0.422, P=0.008) between plasma NT-proBNP and HAMD scores. Altogether, our results indicate that elevated NT-proBNP levels may play a role in linking MDD with increased cardiovascular risk

Endophytic fungi decrease available resources for the aphid Rhopalosiphum padi and impair their ability to induce defences against predators

1. The production of winged morphs is a well known mechanism of induced defence in aphids to escape from natural enemies, and is also a reaction to poor resource quality. 2. Host plants of aphids often associate with endophytic fungi that have been shown to reduce the fitness of some species of aphids. 3. It was hypothesised that endophyte infection of host plants that represent a low quality plant resource should increase the aphid’s induced response to a predator because both low plant quality and predator presence represent a stronger cue for wing production than predator presence alone. 4. In a laboratory experiment, bird cherry-oat aphids Rhopalosiphum padi L. were exposed to the factors predator threat and endophyte infection and the effects of these factors on the proportion of winged morphs produced by the aphid colonies was analysed. 5. The presence of endophytic fungi strongly decreased aphid colony sizes. When a predator threat was present, all colonies on endophyte-free grasses produced winged morphs whereas only a few colonies were able to produce winged morphs on endophyteinfected grasses. However, these few colonies produced larger proportions of winged morphs than colonies on endophyte-free grasses. Without a predator threat, no colonies on endophyte-infected grasses produced any winged morphs. 6. These results show that aphids in stressed conditions and with reduced fitness will only invest in inducible defences when predators are present but are unable to produce winged morphs in response to endophyte presence

Sperm competition affects sex allocation but not sperm morphology in a flatworm

Sperm competition has been shown to be an important evolutionary agent affecting the behaviour, physiology, and morphology of both males and females. One morphological trait that is particularly likely to be affected by sperm competition is sperm size because it is thought to influence the competitiveness of sperm by determining sperm longevity, motility, and/or their ability to displace competing sperm. Most comparative studies across taxa have found a positive relationship between the level of sperm competition and sperm length, but very few studies have tested for a phenotypically plastic adjustment of sperm morphology in response to sperm competition. In this study, we experimentally tested for an effect of sperm competition on phenotypic plasticity in sperm morphology in an obligately outcrossing simultaneous hermaphrodite, the free-living flatworm Macrostomum lignano, by either raising worms in monogamous pairs (no sperm competition) or in promiscuous groups (intense sperm competition). Worms in groups produced larger testes and smaller ovaries as predicted by sex allocation theory and as previously documented in this species. However, we found no evidence for an effect of group size on sperm morphology, measured as total sperm length, sperm body length, and the length of two different sperm appendages. We conclude that M. lignano may either be incapable of adjusting the sperm morphology in a phenotypically plastic way and/or that there might be no benefit of phenotypic plasticity in sperm traits in this species