Impact of low sperm competition on male reproductive trait allometries in a bush-cricket

Winkler L, Kirch LM, Reinhold K, Ramm SA. Impact of low sperm competition on male reproductive trait allometries in a bush-cricket. BMC Evolutionary Biology. 2019;19(1): 185.Background Studying reproductive trait allometries can help to understand optimal male investment strategies under sexual selection. In promiscuous mating systems, studies across several taxa suggest that testes allometry is usually positive, presumably due to strong selection on sperm numbers through intense sperm competition. Here, we investigated testes allometry in a bush-cricket species, Metaplastes ornatus, in which females mate promiscuously, but where sperm removal behaviour by males likely drastically reduces realised sperm competition level. Results As hypothesised, we found evidence for negative testes allometry and hence a fundamentally different male investment strategy compared to species under intense sperm competition. In addition, the mean relative testes size of M. ornatus was small compared to other species of bush-crickets. Surprisingly, the spermatophore gland, a potential alternative trait that males could invest in instead of testes, also did not show positive allometry, but was approximately isometric. We further observed the expected pattern of negative allometry for the male morphological structure responsible for sperm removal in this species, the subgenital plate, supporting the one-size-fits-all hypothesis for intromittent genitalia. Conclusion Our findings suggest that the evolution of sperm removal behaviour in M. ornatus was a key adaptation for avoiding sperm competition, with important consequences for reproductive trait allometries. Nevertheless, they also imply that it does not pay for larger males to invest disproportionately in nuptial gift production in this species

A review of the importance of mineral nitrogen cycling in the plant-soil-microbe system of permafrost-affected soils—changing the paradigm

The paradigm that permafrost-affected soils show restricted mineral nitrogen (N) cycling in favor of organic N compounds is based on the observation that net N mineralization rates in these cold climates are negligible. However, we find here that this perception is wrong. By synthesizing published data on N cycling in the plant-soil-microbe system of permafrost ecosystems we show that gross ammonification and nitrification rates in active layers were of similar magnitude and showed a similar dependence on soil organic carbon (C) and total N concentrations as observed in temperate and tropical systems. Moreover, high protein depolymerization rates and only marginal effects of C:N stoichiometry on gross N turnover provided little evidence for N limitation. Instead, the rather short period when soils are not frozen is the single main factor limiting N turnover. High gross rates of mineral N cycling are thus facilitated by released protection of organic matter in active layers with nitrification gaining particular importance in N-rich soils, such as organic soils without vegetation. Our finding that permafrost-affected soils show vigorous N cycling activity is confirmed by the rich functional microbial community which can be found both in active and permafrost layers. The high rates of N cycling and soil N availability are supported by biological N fixation, while atmospheric N deposition in the Arctic still is marginal except for fire-affected areas. In line with high soil mineral N production, recent plant physiological research indicates a higher importance of mineral plant N nutrition than previously thought. Our synthesis shows that mineral N production and turnover rates in active layers of permafrost-affected soils do not generally differ from those observed in temperate or tropical soils. We therefore suggest to adjust the permafrost N cycle paradigm, assigning a generally important role to mineral N cycling. This new paradigm suggests larger permafrost N climate feedbacks than assumed previously

Divergent testis allometry in two subspecies of the bushcricket Poecilimon veluchianus

Koschmieder M, Müller M, Reinhold K, Ramm SA. Divergent testis allometry in two subspecies of the bushcricket Poecilimon veluchianus. BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY. 2018;124(1):32-40.Static allometry is frequently used as a metric of sexual selection, with traits under strong selection often expected to exhibit positive allometry. Although this appears largely to be true for pre-copulatory traits, such as weapons and ornaments, the allometry of post-copulatory sexually selected traits has seldom been investigated. Here, we explore the evolution of testis allometry between two bushcricket subspecies that have recently diverged in body size and yet still exhibit similar relative investment in testis size. By comparing Poecilimon veluchianus veluchianus with the smaller subspecies P. v. minor, we tested whether this pattern results from conserved isometry or from divergence in either the slope or the intercept of the allometric equation. Based on measurements of 246 males sampled from the wild during the mating season, we found that the similar relative testis size of the two subspecies was not the result of conserved isometric testis scaling and thus not simply explained by recent divergence in body size. Instead, both subspecies exhibited highly similar and positive allometric slopes for testis size (allometric coefficient = 1.4) but differed significantly in the intercept of these slopes. This result hints at an evolutionary constraint conserving the allometric slope between the subspecies but appears to indicate a greater evolvability of the allometric intercept

Strategic Investment in Sperm Removal Behaviour in a Bushcricket

Foraita M, Lehfeldt S, Reinhold K, Ramm SA. Strategic Investment in Sperm Removal Behaviour in a Bushcricket. JOURNAL OF INSECT BEHAVIOR. 2017;30(2):170-179.Multiple mating by females is widespread and generates sperm competition among the ejaculates of rival males over fertilization. One way in which males can avoid or reduce sperm competition is by displacing or removing previous males' sperm from female sperm stores. An apparent example of this occurs in the bushcricket Metaplastes ornatus. Males perform a specialised sperm removal behaviour (SRB), using their highly-derived subgenital plate, with which they remove sperm from the female's spermatheca during the early phases of mating before transferring a spermatophore of their own. Here we investigated whether males strategically invest in SRB according to the amount of previously stored sperm present in females. Each male was tested twice, once with a female containing sperm ('filled' condition) and once with a female from whom most previously deposited sperm had recently been removed by another male (emptied' condition). For comparison, a separate group of males was paired with virgin females. Males did not discriminate between non-virgin females in the 'emptied' or 'filled' conditions in terms of their investment in SRB, suggesting they may not able to perceive the amount of sperm present in the female's spermatheca. By contrast, male investment in SRB was significantly reduced in pairings with virgin females, indicating that males are sensitive to some aspect of a female's mating status. Our results thus suggest that males modulate SRB in response to female-mediated cues, possibly chemical cues left by previous males, which would not be present on virgin but would be on non-virgin females

Male birch catkin bugs vary copula duration to invest more in matings with novel females

Reinhold K, Engqvist L, Consul A, Ramm SA. Male birch catkin bugs vary copula duration to invest more in matings with novel females. Animal Behaviour. 2015;109:161-166

Male birch catkin bugs vary copula duration to invest more in matings with novel females

Recent developments in the study of mating behaviour have emphasized the importance of strategic investment of limited reproductive resources. However, in many cases it can be difficult to interpret traits such as copula duration, because they are interacting phenotypes that ultimately depend upon both the male and female mating partner, and the sexes may frequently disagree over the optimal outcome. Here we report the results of experiments designed to establish which sex controls copula duration in the birch catkin bug, Kleidocerys resedae, and to test for strategic investment by the controlling sex. First, we found that matings of field-caught individuals were relatively short, but that copula duration increased following a period of sexual isolation, reaching a maximum after 2 days. However, copula duration was again shorter in re-pairings of the same individuals 1 h after their first mating. Because these results could be interpreted as a response to sexual isolation by either sex, we next investigated whether copula duration is under male or female control in this species. Experimental pairings between males and females isolated for 1 h or 48 h in all four possible combinations revealed that copula duration depended strongly on the period of male but not of female sexual isolation, implying that this trait is under male control. Finally, if males mated once were re-paired after 1 h with either the same or a novel (but still recently mated) female, we found that they mated for significantly longer with the latter. Collectively, our results imply that male birch catkin bugs in nature are frequently time-, sperm- or seminal fluid-limited, and that, as predicted by theory, they strategically allocate more of their mating effort and ejaculate reserves to novel females, a form of (cryptic) male mate choice