Inter- and intrasexual dimorphism in the diving beetle Hydroporus memnonius Nicolai (Coleoptera: Dytiscidae)

Sexual conflict can drive rapid intersexual arms races, and lead to pronounced sexual dimorphism. Such dimorphism is frequent in diving beetles, where males typically possess expanded front and middle tarsi, supplied with adhesive setae to grasp females during mating, and females often have rough dorsal surfaces which hinder male attachment. In a number of species, females are dimorphic, being either smooth and male-like, or heavily sculptured dorsally. Smooth and sculptured females often have distinct biogeographies, and may be expected to be associated with specific counter-adaptations in males. The European diving beetle, Hydroporus memnonius Nicolai, includes a smooth male-like female, and a matt morph, var. castaneus Aubé, which are largely allopatric in distribution. We show that the two morphs differ in the density and intensity of their surface microreticulation, and that matt females are associated with morphologically distinct males, which have developed specific countermeasures on their tarsi, including a greater number of large adhesive setae, individually larger in area. Such males are expected to be more successful in pairing with both matt and shining females, and it is suggested that a process of population replacement, partly driven by sexual interactions, may occur where the two forms overlap in range.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 685–697.     

Sexual dimorphism and sexual conflict in the diving beetle Agabus uliginosus (L.) (Coleoptera: Dytiscidae)

Sexual conflict can drive intersexual arms races, with female resistance and male persistence traits coevolving antagonistically. Such arms races are well documented in some diving beetles, although the extent of sexual conflict in this family remains unclear. The European dytiscid Agabus uliginosus has a strikingly dimorphic female; individuals from most regions are smooth and male‐like, whereas those from some populations have a strongly roughened dorsum, a trait that has attracted the name dispar. We demonstrate that rough and smooth females differ consistently in the development of dorsal surface microreticulation, and that these females are associated with males that differ in the development of their persistence traits. These findings extend the occurrence of pre‐insemination sexual conflict and associated intrasexual dimorphism in Dytiscidae, and suggest that such mating systems are relatively widespread in these beetles.     

Intraspecific variation and intersexual correlation in secondary sexual characters of three diving beetles (Coleoptera: Dytiscidae)

Male diving beetles of the subfamily Dytiscinae possess tarsi with adhesive discs that they strike on the female dorsum during mating interactions. Females of many species are dimorphic, being either smooth or structured dorsally. Darwin suggested the female structures were an aid for the male but in this study we investigate these characteristics in the light of sexual conflicts. The intraspecific variation in the numbers and size distribution of male tarsal discs, and in body measurements were recorded for three dytiscine species, all with dimorphic females. The number of protarsal discs in the two Dytiscus species varied much more than previously reported. In addition, only a small part of the variation could be explained by body size. In Graphoderus we found highly significant differences in male secondary sexual characters among populations. A multivariate analysis significantly correlated male secondary sexual characters with the proportion of granulate females in the populations. These observations are consistent with the theory of arms races and female counter adaptations. Covariation between male and female characters is predicted from a framework of sexual conflict over mating rate. At the same time our study gives a new perspective on the function of dytiscine female dorsal irregularities debated ever since Darwin.     

Higher‐level phylogeny of diving beetles (Coleoptera: Dytiscidae) based on larval characters

A comprehensive higher‐level phylogeny of diving beetles (Dytiscidae) based on larval characters is presented. Larval morphology and chaetotaxy of a broad range of genera and species was studied, covering all currently recognized subfamilies and tribes except for the small and geographically restricted Hydrodytinae, where the larva is unknown. The results suggest several significant conclusions with respect to the systematics of Dytiscidae including the following: monophyly of all currently recognized subfamilies, although Dytiscinae when considered in a broad context is rendered paraphyletic by Cybistrinae; currently recognized tribes are monophyletic except for Agabini, Hydroporini and Laccornellini; inter‐subfamily and inter‐tribe relationships generally show weak support, except for a few well supported clades; three distinct clades are recognized within Dytiscinae [Dytiscini sensu lato (i.e. including the genera Dytiscus Linnaeus and Hyderodes Hope), Hydaticini sensu lato, and Cybistrini]; and recognition of Pachydrini as a distinct tribe. Other less robust results include: Methlini sister to the rest of Hydroporinae; relative basal position of Laccornini, Hydrovatini and Laccornellini within Hydroporinae; close relationship of Agabinae and Copelatinae; Matinae nested deep within Dytiscidae, as sister to a large clade including Colymbetinae, Coptotominae, Lancetinae and Dytiscinae sensu lato; the sister‐group relationship of Agabetini and Laccophilini is confirmed. The results presented here are discussed and compared with previous phylogenetic hypotheses based on different datasets, and the evolution of some significant morphological features is discussed in light of the proposed phylogeny. All suprageneric taxa are diagnosed, including illustrations of all relevant synapomorphies, and a key to separate subfamilies and tribes is presented, both in traditional (paper) format and as an online Lucid interactive identification key.     

Surviving submerged—Setal tracheal gills for gas exchange in adult rheophilic diving beetles

The gas exchange in adult diving beetles (Coleoptera: Dytiscidae) relies on a subelytral air store, which has to be renewed in regular intervals at the water surface. The dive duration varies from a few minutes to 24 h depending on the species, activity, and temperature. However, some species remain submerged for several weeks. Stygobiont species do not ascend to the surface and gas exchange of these species remains unclear, but it is assumed that they require air filled voids for respiration or they use cutaneous respiration. In this study, we investigate the gas exchange in the running water diving beetle Deronectes aubei, which survive submerged for over 6 weeks. The diffusion distance through the cuticle is too great for cutaneous respiration. Therefore, the dissolved oxygen uptake of submerged beetles was determined and an oxygen uptake via the rich tracheated elytra was observed. Fine structure analyses (SEM and TEM) of the beetles showed tracheated setae mainly on the elytral surface, which acts as tracheal gills. Prevention of the air bubble formation at the tip of the abdomen, which normally act as physical gill in Dytiscidae, resulted in no effect in oxygen uptake in D. aubei, but this was the sole way for a submerged Hydroporus palustris to get oxygen. The setal gas exchange technique explains the restriction of D. aubei to rivers and brooks with high oxygen concentration and it may also be used by subterran living diving beetles, which lack access to atmospheric oxygen. The existence of setal tracheal gills in species in running water which are often found in the hyporheic zone and in stygobiont species supports the known evolution of stygobiont Dytiscidae from species of the hyporheic zone. For species in running water, setal tracheal gills could be seen as an adaptation to avoid drifting downstream by the current. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Securing paternity: mating plugs in the dwarf spider Oedothorax retusus (Araneae: Erigoninae)

One of the various male strategies to prevent or impede female remating is the production of a mating plug that covers the female genital opening or remains inside of the female genital tract after mating. Such structures have been described for many species in many animal taxa; however, in most cases, we know little or nothing about their specific adaptive value. Our investigations demonstrate that females of the dwarf spider species Oedothorax retusus (Westring, 1851) (Linyphiidae, Erigoninae) exhibit a substance on one or both of her paired genital openings only after copulation. We performed double-mating trials and forced the second male to mate into the previously used or unused spermathecal duct of the female by amputating one of his paired male gonopods (pedipalps). Furthermore, to investigate whether the duration of the first mating has an effect on the size and efficiency of the mating plug, we interrupted first matings after either 1 or 3 min, categorized plug size and recorded mating behaviour of subsequent males. The amount of secretion transferred was larger in long compared to short copulations. A long first copulation successfully prevented subsequent males from mating into the used ducts, whereas mating success after short first matings was similar to matings into unused copulatory ducts of the females. The present study demonstrates that a male O. retusus can prevent a rival from transferring sperm into the same spermatheca by applying a mating plug, but only if he mates for long enough.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 574–583.     

Molecular phylogeny of the highly disjunct cliff water beetles from South Africa and China (Coleoptera: Aspidytidae)

The superfamily Dytiscoidea contains six families with an aquatic lifestyle, with most of its extant diversity in two families: the burrowing water beetles (Noteridae) and the diving beetles (Dytiscidae). The other families have few species (up to six) and generally highly disjunct extant distributions. Aspidytidae currently contains one genus with two species, one in China and one in South Africa. Here we provide the first molecular data for the Chinese species, allowing us to explore the phylogenetic relationships and position of both species of this small family for the first time. Based on a matrix of 11 genes we inferred a phylogenetic hypothesis for Dytiscoidea including all extant families. Unexpectedly, Aspidytidae were consistently recovered as paraphyletic relative to Amphizoidae, despite being well characterized by apparently synapomorphic adult features. A re‐examination of larval characters in the two aspidytid species revealed that the larva of the Chinese species is strikingly similar to that of Amphizoidae. Both share a series of plesiomorphic features but also some potential synapomorphies, including a dense vestiture of short setae on the head capsule, anteriorly shifted posterior tentorial grooves and widely separated labial palps. Arguably these features may belong to the groundplan of the clade Aspidytidae + Amphizoidae, with far‐reaching secondary modifications (including reversals) in the South African Aspidytes niobe. At present we retain the family Aspidytidae, however, due to the strong adult morphological synapomorphies of the two extant species, and the fact that the molecular paraphyly of the family may result from the highly divergent nature of the two extant species. This long evolutionary separation and strong divergence, in terms of gene sequences and larval features, is undeniable, substantial levels of saturation in third codon positions of protein‐coding genes being present between the two taxa. We address this issue taxonomically by introducing the new genus S inaspidytes gen. nov. for the Chinese Aspidytes wrasei. The continued contentious relationships amongst Dytiscidae, Hygrobiidae, Aspidytidae and Amphizoidae highlight the need for more data to address dytiscoid phylogenetics, possibly involving a genomic approach. © 2016 The Linnean Society of London     

Seasonal variation in genital and body size, sperm displacement ability, female mating rate, and male harassment in two calopterygid damselflies (Odonata: Calopterygidae)

Sperm competition is a pervasive force. One adaptation is the male ability to displace the rivals' sperm that females have stored from previous copulations. In the damselfly, Calopteryx haemorrhoidalis asturica , males with wider aedeagi displace more spermathecal sperm. The present study documents that the same mechanism operates in another damselfly, Hetaerina americana . However, this genital width in both species decreases along the season, but late-emerging females have more sperm displaced than early-emerging females. Because territorial males mated more and were larger in body and genital size than nonterritorial males, late-season females mated with considerably larger males with respect to female size and this produced higher sperm displacement. Assuming female benefits from storing sperm but that such benefit does not prevail if males displace sperm, it is predicted that, along the season, females will mate less and male harassment (in terms of male mating attempts and oviposition duration) will increase. These predictions were corroborated. In H. americana , it was also tested whether spermathecal sperm became less viable along the season. The results obtained did not corroborate this. This is the first evidence indicating that season affects sperm displacement ability and female mating frequency due to changes in male body and genital size.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 815–829.     

Revising the definition of the crustacean seta and setal classification systems based on examinations of the mouthpart setae of seven species of decapods

The crustacean cuticle has numerous projections and some of these projections, the setae, have important mechanical as well as sensory functions. The setae display a wide diversity in their external morphology, which has led to great problems separating setae from other projections in the cuticle and problems in making a consistent classification system. Here, the cuticular projections on the mouthparts of seven species of decapods are examined by scanning and transmission electron microscopy. A new definition is given: a seta is an elongate projection with a more or less circular base and a continuous lumen; the lumen has a semicircular arrangement of sheath cells basally. From the details of the external morphology the mouthpart setae are divided into seven types: pappose, plumose, serrulate, serrate, papposerrate, simple and cuspidate setae, which are suggested to reflect mechanical functions and not evolutionary history. This classification system is compared with earlier systems.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 142 , 233–252.     

Female alpine newts (Triturus alpestris) mate initially with males signalling fertility benefits

Gametic asymmetry implies that females invest more per gamete than males do and thus sperm is considered to be a relatively cheap resource. However, contrary to this classic view, sperm has been shown to be frequently in short supply; hence, selection favouring females that mate for fertility benefits should occur. For this reason, we determined whether males signalling fertility are preferred by female newts of the species Triturus alpestris . We performed paired female–male trials using unmated and previously inseminated females to determine potential criteria for female interest in a courting male, to establish what factors lead to successful mating and to assess the importance of female choice for direct and indirect benefits. We found that female interest in any potential mate and mating success decreased once mating had occurred. Furthermore, we detected an increase in spermatophore deposition rate and rapid spermatophore transfer in encounters that resulted in a successful mating. The results obtained indicate that female alpine newts are attracted to males showing signs of relatively high fertility and that females exhibit a decreased propensity to mate once initial sperm reserves have been acquired. Our results support the theory of initial female choice for fertility benefits.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 483–491.