Energy beyond the pupal stage: larval nutrition and its long-time consequences for male mating performance in a scorpionfly

The basic requirement for selection to take effect is variation in fitness relevant traits among individuals of a population. This study is concerned with the question whether environmental conditions met during an early phase of life history that is dominated by the natural component of selection will affect traits and behaviour in a sexual selection context after metamorphosis in a holometabolous insect species. We examined the effects of nutrition as a proximate factor responsible for intrasexual phenotypic variation in the mating performance of male Panorpa vulgaris (Mecoptera: Panorpidae). For this purpose, we manipulated food availability during larval development as well as during adulthood. To obtain matings and to increase their reproductive success males must secrete salivary masses which are then consumed by the females during copulation. The results of the present study are consistent with those of previous studies demonstrating a strong effect of nutrition during adulthood on various fitness relevant traits (salivary gland development, saliva investment in copulations, etc.). But moreover, we could show that food availability during larval development affected male body weight and that there was an interaction between larval and adult diet affecting salivary gland weight relative to body weight. Therefore, food availability during the larval stage can become an important and limiting factor for salivary gland development (and mating success) depending on food availability during adulthood. Several other variables (number of salivary masses, copulation duration, salivary mass weight and saliva investment) seemed not to be associated with larval nutrition.     

Embryonic development of the scorpionfly Panorpa emarginata Cheng with special reference to external morphology (Mecoptera: Panorpidae)

The Mecoptera are thought to be one of the most primitive groups in the Holometabola, but their embryology is rarely studied. By means of scanning electron microscopy, we studied the external features of the embryo of the scorpionfly Panorpa emarginata in middle and late development. The embryo remains in the superficial position until hatching. Embryonic development can be divided into 10 stages along with the first‐instar larva. The external features are described from the germ band to the first‐instar larva, with special reference to the components and segmentation of the head, the segmentation of abdomen and the formation of abdominal prolegs. Our results confirm that the head consists of an anterior‐most acron and six trunk segments: the labral, antennal, intercalary, mandibular, maxillary, and labial segments. The labrum is confirmed to derive from the paired appendages. Our observations also provide additional direct evidence that the abdominal prolegs are not serially homologous with the thoracic legs. The presence of the eleventh abdominal segment is clarified. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

太白蝎蛉消化道形态学与组织学研究

利用光学显微镜和扫描电子显微镜, 在形态学和组织学水平上研究了太白蝎蛉Panorpa obtusa Cheng成虫消化道的结构。结果表明： 蝎蛉消化道由前肠、中肠、和后肠组成。前肠包括咽喉、食道、和前胃, 但没有嗉囊,其中咽喉可分为骨化的前咽和附着扩肌的后咽（咽喉唧筒）; 前胃壁很厚,内膜上长有许多排列整齐、紧密的棕色胃刺,司过滤、暂时储存和磨碎食物的功能; 前肠末端有6个贲门瓣伸入中肠。中肠较长且膨大,其肠壁细胞由柱状细胞和再生细胞组成; 肠壁细胞外分别为环肌和纵肌,无胃盲囊,也未观察到围食膜。6根棕红色的马氏管位于中、 后肠分界处。后肠分为不对称的“V”字型回肠、环状结肠、以及膨大透明的直肠, 直肠内壁上有6个交替排列的直肠垫。最后简要讨论了蝎蛉消化道的结构与功能,及其在蝎蛉科昆虫分类中的意义。     

Environment-dependent genetic correlations between development time and body mass in a scorpionfly

Development time and body mass at maturation are two important fitness traits fundamental for our understanding of life history theory. Generally, fast development is associated with small adult body mass, as it will take longer to grow large. However, the strength of this trade-off may depend on average food availability, as the potential benefit of long development will depend on the rate of food intake. Here, I report results of a food manipulation experiment during larval development of the scorpionfly Panorpa cognata (Insecta, Mecoptera). Development time showed considerable genetic variation, yet food level had no influence and there was a strong genetic correlation in development time across environments. As expected, larval and adult body weight was significantly affected by food availability. Furthermore, body mass was influenced by a highly significant genotype-by-environment interaction. The reaction norm for body mass in response to food treatment was much stronger in families with long development time compared with rapidly developing genotypes. This effect was accompanied by a shift in the genetic correlation between development time and body size when comparing the two food levels. Specifically, the genetic correlation between body mass and development time changed from being positive at high food levels to a negative genetic correlation at low food levels. These results are consistent with other empirical findings demonstrating a similar shift in genetic correlations between body mass and development time when comparing favourable and unfavourable environmental conditions.     

Histology and ultrastructure of the salivary glands and salivary pumps in the scorpionfly Panorpa obtusa (Mecoptera: Panorpidae)

Liu, S. and Hua, B. 2009. Histology and ultrastructure of the salivary glands and salivary pumps in the scorpionfly Panorpa obtusa (Mecoptera: Panorpidae). —Acta Zoologica (Stockholm) 91 : 457–465. The morphology, histology and ultrastructure of the salivary glands and salivary pumps in the scorpionfly Panorpa obtusa Cheng 1949 were investigated using light microscopy and scanning and transmission electron microscopy. The salivary glands display a distinct sexual dimorphism. The female has only two small sac‐like glands located in the prothorax, while the male possesses six long tubular glands extending into the sixth abdominal segment. The male salivary glands can be divided into five distinct regions. The apical long, thin secretory region possesses numerous secretory cells containing large secretory vesicles; the salivary reservoir expands in diameter, accumulating and temporarily storing the saliva in addition to secreting saliva; the constricted region contains prismatic cells with complex infolded plasma membrane; the sac has an internal brush border to absorb water and ions; the common salivary duct contains longitudinal muscles in the male, but not in the female. The salivary pump possesses independent strong dorsal muscles and abundant internal palm spines near its orifice. The anatomy and ultrastructure of the salivary glands and the salivary pump of scorpionflies as well as their possible functions are briefly discussed.     

Taxonomic revision and phylogenetic analysis of the enigmatic scorpionfly genus Leptopanorpa MacLachlan (Mecoptera: Panorpidae)

The representatives of the enigmatic genus Leptopanorpa MacLachlan are characterized by exaggeratedly elongated male abdomens and are likely endemic to Java and Sumatra, Indonesia. Here, we present a taxonomical revision of 14 species of Leptopanorpa, including two new species: Leptopanorpa linyejiei sp. n. from West Java and Leptopanorpa majapahita sp. n. from East Java. A key to species of Leptopanorpa is provided. Leptopanorpa sieboldi MacLachlan is treated as a junior synonym of Leptopanorpa charpentieri (Burmeister), and Leptopanorpa pi decorata Lieftinck is synonymized with Leptopanorpa pi (van der Weele). Leptopanorpa peterseni Lieftinck is reported from Bali for the first time. In order to unravel the phylogeny of Leptopanorpa and other groups with elongated male abdomens, maximum parsimony and Bayesian inference analyses were performed based on 61 morphological characters and partial sequences of one nuclear gene (28S ribosomal RNA) and two mitochondrial genes (cytochrome c oxidase subunits I and II). Thirty-three species in Panorpoidea were selected as in-group taxa and two species in Choristidae as out-group taxa. The results highly support a monophyletic Leptopanorpa, which nests within a paraphyletic Neopanorpa van der Weele. Both parsimonious and Bayesian results suggest that Leptopanorpa can be divided into four subclades. We elucidated the evolutionary history of Leptopanorpa with regard to the paleogeological events of Sundaland and corroborated the multiple origins of elongated male abdomens in Panorpoidea. We also hypothesized that the ventral hook on the male abdominal sternum VI of L. linyejiei sp. n. is very likely used to control the female's abdomen during copulation.     

We do not select,nor are we choosy: reproductive biology of Strepsiptera (Insecta)

The cryptic entomophagous parasitoids in the order Strepsiptera exhibit specific adaptations to each of the 34 families that they parasitize, offering rich opportunities for the study of male–female conflict. We address the compelling question as to how the diversity of Strepsiptera (where cryptic speciation is common) arose. Studying 13 strepsipteran families, including fossil taxa, we explore the genitalic structures of males, the free‐living females of the Mengenillidia (suborder), and the endoparasitic females of the Stylopidia (suborder). Inferring from similarity between aedeagi of males either between congeners, heterogeners, or between species within the same taxonomic family, the same of which is true of the cephalothoraces of females, we predict that male–female conflict and a co‐evolutionary morphological arms race between sexes is not likely to exist in most species of Strepsiptera. We then review the non‐genitalic structures that play a role during sexual communication, and present details of copulatory behaviour. We conclude that Strepsiptera fall within the synchronous sensory exploitation model where short‐lived males take advantage of a pre‐existing sensory system involving pheromone signals emitted by females.     

Opposing selection on a sexually dimorphic trait through female choice and male competition in a water boatman

Female choice and male-male competition are traditionally considered to act in concert, with male competition facilitating female choice. This situation would enforce the strength of directional selection, which could reduce genetic variation and thus the benefits of choice. Here I show that in a water boatman, Sigara falleni, the direction of selection through female choice and male competition vary among traits under laboratory conditions. The two forces were mutually enforcive in acting on body size but exerted opposing selection on a sexually selected trait, male foreleg pala size. Female choice favored large palae, whereas male competition favored smaller palae, suggesting that large palae are costly in competition. This conflicting selection through female choice and male competition could be one of the forces that contribute to the maintenance of genetic variation in sexually selected traits.     

Genital morphology and taxonomy of the water strider Aquarius remigis (Say) (Insecta, Hemiptera-Heteroptera: Gerridae)

The shape of the dorsal vesical plate was used to determine the extent of morphological differentiation among populations of the water strider Aquarius remigis (Say) (Hemiptera-Heteroptera: Gerridae), and between species assigned to the A. remigis species group. Populations were sampled throughout North America and Mesoamerica, and included paratypes of A. remigoides Gallant & Fairbairn, and material collected from the type localities of A. amplus (Drake & Harris) and A. nyctalis (Drake & Hottes). If taxonomy is to be inferred from the shape of the dorsal vesical plate, as suggested by previous authors, several taxonomic issues need to be reconsidered. First, there was one species distributed widely across North America and deep into Mexico that is very likely to represent A. remigis , meaning that populations from the western USA previously assigned to ' A. nyctalis ' should be synonymized with this species. Second, A. remigoides as currently defined also includes some populations of A. remigis , and is probably much less widely distributed in the south-eastern USA than previously thought. A hybridization zone in Pennsylvania between A. remigis and A. remigoides , as inferred from measurements of body size and allozyme electrophoresis, is not congruent with data from the male genitalia, which indicated a transition zone between the two forms in Virginia much further to the south. Finally, A. amplus was widespread in Mexico, reaching into Guatemala to the south and into Arizona to the north.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 381–398.     

Evolution of a sexually dimorphic trait in a broadly distributed topminnow (Fundulus olivaceus)

Understanding the interaction between sexual and natural selection within variable environments is crucial to our understanding of evolutionary processes. The handicap principle predicts females will prefer males with exaggerated traits provided those traits are indicators of male quality to ensure direct or indirect female benefits. Spatial variability in ecological factors is expected to alter the balance between sexual and natural selection that defines the evolution of such traits. Male and female blackspotted topminnows (Fundulidae: Fundulus olivaceus) display prominent black dorsolateral spots that are variable in number across its broad range. We investigated variability in spot phenotypes at 117 sites across 13 river systems and asked if the trait was sexually dimorphic and positively correlated with measures of fitness (condition and gonadosomatic index [GSI]). Laboratory and mesocosm experiments assessed female mate choice and predation pressure on spot phenotypes. Environmental and community data collected at sampling locations were used to assess predictive models of spot density at the individual, site, and river system level. Greater number of spots was positively correlated with measures of fitness in males. Males with more spots were preferred by females and suffered greater mortality due to predation. Water clarity (turbidity) was the best predictor of spot density on the drainage scale, indicating that sexual and natural selection for the trait may be mediated by local light environments.     

Mating distribution and its temporal dynamics affect operational sex ratio: a simulation study

The present study investigated how variation in mating distribution in time and among males influences the operational sex ratio (OSR) with a simulation inspired by paternally caring fish. Varying (1) the potential reproductive rate of each sex, (2) the mating distribution among males, and (3) the length of male mating phase, we created different mating patterns. In each case, we searched for the adult sex ratio that resulted in an OSR of 50% (where sex-roles switch). This approach enabled a comparison with a previous model. We found that the OSR was influenced by the distribution of matings in time and among males when the male mating phase was limited by a parental phase. Furthermore, the mating dynamics were shaped by the fact that the numbers of males and females and their capacities for collateral investment affected OSR immediately from the start of the reproductive season, whereas their times-out had a delayed effect on OSR.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 551–559.     

Optic lobes of the larval and imaginal scorpionfly Panorpa vulgaris (Mecoptera,Panorpidae): A neuroanatomical study of neuropil organization,retinula axons,and lamina monopolar cells

Panorpa larvae possess stemmata (lateral ocelli), which have the structure of compound eyes, and stemma lamina and stemma medulla neuropils. A distinct lobula neuropil is lacking. The stemma neuropils have a columnar organization. They contain lamina monopolar cells, and both short and long visual fibers. All the identified larval monopolar neurons have radially arranged dendrites along the entire depth of the lamina neuropil and a single terminal arborization within the medulla (L1/L2-type). The terminals of visual fibers have short spiny lateral projections. Long fibers possess en passant synapses within the lamina. The same principles of organization of first and second order visual neuropils are found in Panorpa imagines. In contrast to the larvae, a lobula neuropil is present. Adults have monopolar cells of the L1-type that are similar to the L1-neurons found in Diptera. The columnar organization, the presence of short and long visual fibers, and lamina monopolar neurons are thus features common to both visual systems, viz., the larval (stemmata) and the imaginal (compound eyes).     

Developmental instability as phenodeviance in a secondary sexual trait increases sharply with thermal stress

Abstract We test for effects of thermal stress applied to pupal flies from Noumea (New Caledonia) and Taipei (Taiwan) on developmental instability (DI) in the male sex comb of Drosophila bipectinata, as well as on pre‐adult survivorship and adult body size. The temperature treatments were Low (25 °C), High (29 °C) and Variable (18 h at 29 °C, 6 h at 34 °C). Although the Variable treatment reduced survivorship and body size, absolute comb size and fluctuating asymmetry generally were invariant across treatments. In contrast, comb phenodeviance increased with stress in both populations. Phenodeviance in one comb segment (C2) increased sharply with stress, whereas phenodeviance in a second major segment (C1) also increased with stress but only in Noumea flies. A major conclusion is that phenodeviations induced in a secondary sexual trait reflect the developmental environment that also damages fitness components, a foundation stone of the hypothesis that expressions of DI reveal phenotypic quality in sexual selection.     

Experimental evolution under varying sex ratio and nutrient availability modulates male mating success in Drosophila melanogaster

Biased population sex ratios can alter optimal male mating strategies, and allocation to reproductive traits depends on nutrient availability. However, there is little information on how nutrition interacts with sex ratio to influence the evolution of pre-copulatory and post-copulatory traits separately. To address this omission, we test how male mating success and reproductive investment evolve under varying sex ratios and adult diet in Drosophila melanogaster, using experimental evolution. We found that sex ratio and nutrient availability interacted to determine male pre-copulatory performance. Males from female-biased populations were slow to mate when they evolved under protein restriction. By contrast, we found direct and non-interacting effects of sex ratio and nutrient availability on post-copulatory success. Males that evolved under protein restriction were relatively poor at suppressing female remating. Males that evolved under equal sex ratios fathered more offspring and were better at supressing female remating, relative to males from male-biased or female-biased populations. These results support the idea that sex ratios and nutrition interact to determine the evolution of pre-copulatory mating traits, but independently influence the evolution of post-copulatory traits.     

Size and mating success in males of the western harvester ant,Pogonomyrmex occidentalis (Hymenoptera: Formicidae)

Mating success in males of the lek mating ant species,Pogonomyrmex occidentalis, increases with increased body size. We estimated the magnitude of the selection coefficients on components of size by collecting males in copula and comparing their morphology to that of males that were collected at the lek but that were not mating. Four characters, body mass, head width, wing length, and leg length, were measured for a sample of 225 mating and 324 nonmating males and 225 females. Significant direct selection favors increased wing length and leg length. Multiple regression of transformed variables (principal components) indicated that the increased mating success of larger males is a function of all four characters. We found no evidence of positive assortative mating on the basis of any individual character or on the multivariate general size variable (the first principal component).     

Sex‐specific effects of inbreeding in wild‐caught Drosophila melanogaster under benign and stressful conditions

In animal populations, sib mating is often the primary source of inbreeding depression (ID). We used recently wild‐caught Drosophila melanogaster to test whether such ID is amplified by environmental stress and, in males, by sexual selection. We also investigated whether increased ID because of stress (increased larval competition) persisted beyond the stressed stage and whether the effects of stress and sexual selection interacted. Sib mating resulted in substantial cumulative fitness losses (egg to adult reproduction) of 50% (benign) and 73% (stressed). Stress increased ID during the larval period (23% vs. 63%), but not during post‐stress reproductive stages (36% vs. 31%), indicating larval stress may have purged some adult genetic load (although ID was uncorrelated across stages). Sexual selection exacerbated inbreeding depression, with inbred male offspring suffering a higher reproductive cost than females, independent of stress (57% vs. 14% benign, 49% vs. 11% stress).     

Evidence for small scale variation in the vertebrate brain: mating strategy and sex affect brain size and structure in wild brown trout (Salmo trutta)

The basis for our knowledge of brain evolution in vertebrates rests heavily on empirical evidence from comparative studies at the species level. However, little is still known about the natural levels of variation and the evolutionary causes of differences in brain size and brain structure within‐species, even though selection at this level is an important initial generator of macroevolutionary patterns across species. Here, we examine how early life‐history decisions and sex are related to brain size and brain structure in wild populations using the existing natural variation in mating strategies among wild brown trout (Salmo trutta). By comparing the brains of precocious fish that remain in the river and sexually mature at a small size with those of migratory fish that migrate to the sea and sexually mature at a much larger size, we show, for the first time in any vertebrate, strong differences in relative brain size and brain structure across mating strategies. Precocious fish have larger brain size (when controlling for body size) but migratory fish have a larger cerebellum, the structure in charge of motor coordination. Moreover, we demonstrate sex‐specific differences in brain structure as female precocious fish have a larger brain than male precocious fish while males of both strategies have a larger telencephalon, the cognitive control centre, than females. The differences in brain size and structure across mating strategies and sexes thus suggest the possibility for fine scale adaptive evolution of the vertebrate brain in relation to different life histories.     

Immunity and the expression of a secondary sexual trait in a horned beetle

Resource-based trade-offs are known to be important in determininginvestment in both sexual ornamentation and immunity in insects.Because of the strict resource limitation experienced duringmetamorphosis, we predict that if insects are trading off ornamentsize and immunity this should be most apparent immediately aftereclosion and that the relationship between sexual ornament sizeand immunity should change with maturation feeding because ofthe changing patterns of resource availability during this process.We therefore present an investigation into the relationshipbetween morphology, sex, and two measures of immune response(phenoloxidase [PO] activity and encapsulation ability) in thehorned beetle Euoniticellus intermedius, immediately after eclosionand after maturation feeding. Both measures increased with maturation,with sex differences in PO activity becoming discernable aftermaturation feeding. PO activity was positively correlated withhorn length in male beetles both on eclosion and after maturationfeeding, and encapsulation ability was positively correlatedwith elytra length. We conclude that resource limitation inthe pupating insect does have effects on immunity but that thisresource limitation does not translate into a measurable trade-offbetween horn length and immunity. The correlation between hornlength and PO activity may arise because both horn length andPO activity are correlated with the same elements of the animal'sbiology that allow some animals both to grow a long horn andto sustain a higher level of PO activity.