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Aim: Local environmental selection and lineage admixture have long been accepted as important adaptive mechanisms in adjusting widespread taxa to new environments. We studied a pond skater, Gerris latiabdominis, to explore the relative roles played by these two mechanisms in its process of adaptation to heterogeneous landscapes. Location: East Asia. Taxon: Gerris latiabdominis Miyamoto, 1958. Methods: Mitochondrial (COI, COII) and nuclear (ddRAD‐seq) markers were sequenced from 202 individuals. Phylogenetic and phylogeographical analyses were conducted to reveal the population genetic structure. The demographical history was simulated by approximate Bayesian computation (ABC). The single‐nucleotide polymorphisms (SNPs) that may have been subjected to natural divergent selection among the populations were assessed, and the recent migration rates were estimated. Finally, shifts in suitable habitat from the last interglacial (LIG) to the present were predicted through ecological niche modelling (ENM). Results: We found population structures inferred from both mitochondrial and nuclear genomes to be almost coincident and to correspond to temporal or spatial heterogeneity. The early Pliocene splitting event between the northern (NO) and southeastern (SE) groups is consistent with the 'arid belt hypothesis', followed by local environmental selection. Approximate Bayesian computation and gene flow estimation strongly suggested that the southwestern (SW) groups originated from a lineage admixture event between the SE and western (WE) groups and subsequently underwent ongoing gene flow from the SE group during the Pleistocene. The mito‐nuclear discordance pattern in the SW group was probably due to the ancient mitochondrial differentiation. Main conclusion: Our results suggest that both local environmental selection and lineage admixture acted as significant mechanisms of G. latiabdominis adaptation to heterogeneous landscapes in East Asia. Furthermore, this study showed that conclusions based exclusively on mitochondrial data might mislead taxonomic, phylogenetic and phylogeographical studies. [ABSTRACT FROM AUTHOR]

Size‐assortative mating, defined as a positive linear association of body size between members of mating pairs, can arise from mechanical constraints on pairing efficiency, particularly when mating success is affected by males' mate‐grasping force. In this context, female resistance is predicted to have an important role in changing the threshold force necessary for males to hold females, thereby contributing to the effect of mechanical constraints. Thus, increased female resistance is expected to increase the paring success of an optimally sized male relative to the female body size (sexual size ratio = male body size/female body size = 0.86), which leads to positive size‐assortative mating. However, very little is known about the extent to which female resistance affects mechanical constraints on mate grasping. Here, using the water strider Gerris gracilicornis (Hemiptera: Gerridae), we tested whether the level of female resistance affected the relationship between the sexual size ratio and latency to pair. We found that optimally sized males mated sooner than other males when females resisted a male's mating attempts. When females did not resist, an effect of sexual size ratio on latency to pair was not found. Our results thus imply that increased female resistance to male mating attempts may strengthen the pattern of size‐assortative mating. We provide clear empirical evidence that female resistance to mating influences the effect of mechanical constraints on size‐assortative mating under sexual conflict. This result further suggests that patterns of size‐assortative mating can be altered by a variety of ecological circumstances that change female resistance to mating in many other animal species under sexual conflict. Relationship between a range of male body size relative to female body size (sexual size ratio) and threshold force (dotted lines) necessary for males to successfully grasp females at the initiation of mating. The threshold force is high when females resist more, and there is a narrowing of the optimal male size range (relative to a certain female size) that leads to a successful initiation of mating. This is expected to result in a strong size‐assortative mating pattern. [ABSTRACT FROM AUTHOR]

There exist surprisingly few marine insects, most of which are confined to the intertidal zone. Halobates is the only genus to have some oceanic species along with some coastal species. Among the coastal sea skaters, that is, genus Halobates and its close relative, genus Asclepios, there are variations in their affinity for the shore. We have studied the distributions of two endangered Japanese sea skaters, Halobates matsumurai and Asclepios shiranui in Kujukushima, where they cooccur in coves. To compare their survival strategies at sea, we especially noted differences in their distributions along the shore during high and low tides. The results show that A. shiranui tended to remain along the shore during low tide. This species appeared to cling to the shore against the ebb current and to stay in the protected coves. By contrast, H. matsumurai tended to leave the shore during low tide. Notably, some adults were found skating outside the coves. The strategy of H. matsumurai appeared to be leaving with the ebb current even beyond the coves, thereby using more resources and enlarging its habitat. Some such coastal Halobates might have acquired the ability to live on the open ocean clearly independent of the shoreline. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Palaeoclimatic and palaeogeological events have been identified as two main factors that influence the genetic structuring of extant organisms. We studied a montane stream‐dwelling insect, Metrocoris sichuanensis, to explore the relative roles played by these two factors in population genetic connectivity. Location: Sichuan Basin, China. Methods: Mitochondrial (COI, COII, Cytb, 16S) and nuclear (EF‐1α, ITS1) markers were sequenced from 208 individuals. Suitable habitat shifts from the Last Glacial Maximum (LGM) to the present were predicted through fine‐tuned ecological niche modelling (ENM). Phylogenetic and phylogeographical analyses were conducted to reveal the population genetic structure. Intraspecific divergence and expansion times were estimated using beast. Finally, the least cost path (LCP) method coupled with migrate analysis was used to identify possible dispersal corridors and estimate the asymmetric gene flow. Results: Our ENM results suggested that population habitat connectivity did not change both in the LGM and current conditions. Whole haplotypes were separated into four highly supported clades/haplogroups that exhibited strong geographical structure. The splitting events between the four lineages likely date back to the Early Pleistocene. Bayesian skyline plot (BSP) indicated a moderate demographic growth from the LGM to the present. A putative dispersal corridor was detected along the Longmen Mountains thrust belt, with unidirectional gene flow from north to south. Main conclusion: Our findings support the geographical isolation of the genetic lineages and a deep early Pleistocene split in M. sichuanensis. Landscape connectivity analysis incorporating the genetic data and the ENM prediction revealed that population genetic connectivity was strongly associated with stable climatic habitats shaped by complex topography. The drainage system might have assisted the rapid movement of populations along the Longmen Mountains thrust belt. A strategy for researching the population genetic connectivity of narrow endemics, such as M. sichuanensis, in global biodiversity hotspots is proposed and discussed in this paper. [ABSTRACT FROM AUTHOR]

Some of the strongest examples of a sexual 'arms race' come from observations of correlated evolution in sexually antagonistic traits among populations. However, it remains unclear whether these cases truly represent sexually antagonistic coevolution; alternatively, ecological or neutral processes might also drive correlated evolution. To investigate these alternatives, we evaluated the contributions of intersex genetic correlations, ecological context, neutral genetic divergence and sexual coevolution in the correlated evolution of antagonistic traits among populations of Gerris incognitus water striders. We could not detect intersex genetic correlations for these sexually antagonistic traits. Ecological variation was related to population variation in the key female antagonistic trait (spine length, a defence against males), as well as body size. Nevertheless, population covariation between sexually antagonistic traits remained substantial and significant even after accounting for all of these processes. Our results therefore provide strong evidence for a contemporary sexual arms race. [ABSTRACT FROM AUTHOR]

Gondwanan vicariance, long-distance dispersal ( LDD), and boreotropical migration have been proposed as alternative hypotheses explaining the pantropical distribution pattern of organisms. In this study, the historical biogeography of the pond skater genus Limnogonus was reconstructed to evaluate the impact of biogeographical scenarios in shaping their modern transoceanic disjunction. We sampled almost 65% of recognized Limnogonus species. Four DNA fragments including 69 sequences were used to reconstruct a phylogram. Divergence time was estimated using a Bayesian relaxed clock method and three fossil calibrations. Diversification dynamics and ancestral area reconstruction were investigated by using maximum likelihood and Bayesian approaches. Our results showed the crown group of Limnogonus originated and diversified in Africa in the early Eocene (49 Ma, HPD: 38-60 Ma), subsequently expanding into other regions via dispersal. The colonization of the New World originated from the Oriental Region probably via the Bering Land Bridge in the late Eocene. Two split events between the Old World and New World were identified: one between Neotropics and Oriental region around the middle Oligocene (30 Ma, HPD: 22-38 Ma), and the other between Neotropics and Africa during the middle Miocene (14 Ma, HPD: 8-21 Ma). The evolutionary history of Limnogonus involved two biogeographical processes. Gondwanan vicariance was not supported in our analyses. The diversification of Limnogonus among Africa, Oriental, and Neotropical regions corresponded with the age of land bridge connection and dispersed as a member associated with the broad boreotropical belt before local cooling (34 Ma). The current transoceanic disjunctions in Limnogonus could be better explained by the disruption of 'mixed-mesophytic' forest belt; however, the direct transoceanic LDD between the Neotropics and Africa could not be ruled out. In addition, the ' LDD' model coupled with island hopping could be a reasonable explanation for the diversification of the Oriental and Australian regions during the Oligocene. [ABSTRACT FROM AUTHOR]

The dietary dependence on volant aquatic insects of eight species of predatory arthropods from three different orders was determined by stable isotope analyses in combination with three-source, two-isotope (C and N) Bayesian mixing models. The predators were collected from riparian zones along three streams in tropical Hong Kong during both the wet and dry seasons. Dietary importance of aquatic insects varied according to predator hunting modes, and showed a consistent pattern across all sites during the wet season. The web-building tetragnathid spider ( Orsinome diporusa) had the greatest reliance (~40-55%) on this water-to-land subsidy, followed by two species of damselflies (40-50%), three cursorial spiders (Lycosidae, Pisauridae, and Sparassidae: 32-51%) and two neustic gerrids (17-36%). Such reliance also varied according to the microhabitat preferences of different cursorial spiders. Four species of predators (gerrids and cursorial spiders) that were active year-round showed generally consistent reliance on aquatic insects between seasons, which probably reflected the observed lack of seasonal variability in the relative proportions of aquatic and terrestrial prey. There was a marked overlap in isotopic signatures of aquatic and terrestrial prey at all sites which, combined with the absence of data on the extent to which isotopic fractionations may vary among individual species of prey and predators, contributes some uncertainty to the estimates of dietary compositions derived by mixing models. The findings of the present study are thus likely to be indicative rather than definitive. [ABSTRACT FROM AUTHOR]

Feeding behavior has been investigated several times in different semiaquatic bugs ( Heteroptera: Gerromorpha), but has never been directly compared between species from lentic and lotic habitats and different families. Time required to capture prey was investigated in five gerromorphan species: A quarius paludum, G erris lacustris, G. odontogaster ( Gerridae), V elia caprai and V. gridellii ( Veliidae). This experiment used live and dead prey and intact and artificially blinded bugs. The presence of vibrational stimuli (live prey) significantly decreased latency to capture prey in all species except G. odontogaster. This species was the only one where visual stimuli affected the response significantly (only with dead prey). Latency to capture in V elia spp. was significantly shorter than that in the three gerrid species. Capture efficiency differed significantly between G erris and V elia spp.; both V elia species carried out unsuccessful attack attempts less frequently than did the G erris species. Prey capture was quicker in treatments with live prey and/or intact bugs. No difference in capture efficiency was found between sexes. A quarius and G erris species from predominantly lentic habitats needed more time to capture prey than did V elia species, which live mostly in streams. This difference in feeding behavior can probably allow coexistence of gerrids and veliids at sites where their occurrence overlaps. [ABSTRACT FROM AUTHOR]

In many egg-laying species, females avoid ovipositing at sites where the predation risk is high. Previous studies have mainly focused on the risk for offspring. The effect of predation risk for the females has been considered in some taxa in which parents spend much time at an oviposition site for parental care or mating (e.g., birds, amphibians). In species in which females do not perform activities other than oviposition at sites, the effect of predation risk for females on oviposition site selection has been rarely investigated. We examined whether the predation risk for ovipositing females affects the decision on oviposition in the water strider Aquarius paludum insularis ( Motschulsky) ( Heteroptera: Gerridae). Adult A. paludum are preyed upon by a backswimmer, Notonecta triguttata ( Motschulsky) ( Heteroptera: Notonectidae), but N. triguttata does not prey upon eggs or early instars of A. paludum. We allowed female A. paludum to oviposit under one of three conditions: in presence of N. triguttata, in presence of its chemicals, and in absence of the predator or its cues (control). Female A. paludum less frequently oviposited in presence of N. triguttata than in its absence. Oviposition frequency did not differ between females in presence of chemicals of N. triguttata vs. those in the control. Female A. paludum recognized the predation risk upon themselves from the presence of N. triguttata and avoided ovipositing. This study is the first to directly show that the predation risk upon ovipositing females changes oviposition site selection in species in which the time spent at an oviposition site is short. [ABSTRACT FROM AUTHOR]

The abundance patterns of two insects, Gerris spinolae and Brachydeutera longipes, were found to be affected by abiotic aquatic factors including free carbon dioxide, dissolved oxygen, BOD, and phosphate concentrations prevailing in four tropical freshwater ponds, three of which being anthropogenically stressed. Regression analysis between each individual-independent water quality variable and insect abundance demonstrated a significant positive correlation in each case between B. longipes abundance and BOD, phosphate, free CO2, and algae dry weight, while a significant negative correlation of each of these variables was found with Gerris spinolae abundance. Moreover, a significant negative correlation of B. longipes abundance was calculated with dissolved oxygen concentration, while G. spinolae abundance exhibited a positive correlation with the same. Thus, G. spinolae appears to be a pollution sensitive, effective bioindicator for healthy unpolluted ponds, while B. longipes has potential as a pollution-resistant insect species indicative of pollution occurrence. [ABSTRACT FROM AUTHOR]

Sea skaters Halobates matsumurai Esaki and Asclepios shiranui (Esaki) are among the few marine insects found in Japan. For the past several decades, they have become rare in most localities and have now been designated as endangered by the government. In order to understand their adaptive strategies to the marine environment and to develop conservation measures, it is essential to know their life histories. We studied their lifecycles in Kujukushima Bay off the north coast of Kyushu (Japan) where they cooccurred in small coves along the jagged coast. They appeared to have more than one generation a year and to overwinter in the egg stage. Eggs of H. matsumurai were laid on natural sandstones and man-made sandstone walls along the shore, mostly above the average sea level. The eggs had very hard shells, presumably adaptive to protect them from desiccation, solar radiation, and wave action, especially during the overwintering period. [ABSTRACT FROM AUTHOR]

Seasonal records of nymphs of the water strider Aquarius paludum Fabricius (Heteroptera: Gerridae) at a waterway in Kochi prefecture, Japan (33°00′N to 33°30′N), in 2007, show that populations of new generation adults occur four or more times during the year, in mid and late May; late July to early August; September; and October to November. In laboratory experiments, more than 50% of adults are reproductive, irrespective of photoperiod, and this ratio increases to 80% even under a short-day LD 11.5 : 13.5 h photocycle, which corresponds to the winter season at Kochi (33°N). There is a diminishing photoperiodic response in relation to the induction of diapause compared with measurements made in previous years (1995-1997), suggesting that reproduction may be possible over a much longer period in the near future (and even in winter) if local climate warming is sustained. A high proportion of males sampled in 2008 have small testes and a high proportion of females do not have mature oöcytes even in summer. This contrasts with earlier data showing that the testis volume index for the same period is greater in 1995-1997, and that 75% of females have mature oöcytes. These changes suggest that the Kochi-Nankoku population of A. paludum is beginning to show partial aestivation. Overwintering adults of both sexes are found to have no mature flight muscles in October/November 2008. This is in marked contrast with earlier data from 1995 and 2004. Adults that are reared in the laboratory also show a lower flight propensity in response to shorter day lengths. The absence of mature flight muscles in the autumn and lower flight propensity under shorter days may indicate a cessation of dispersal between the summer habitats and overwintering sites on land far from the waterways. Taken together, these data suggest that populations of A. paludum in the Kochi-Nankoku region are continuing to show adaptive changes, apparently in relation to global warming. [ABSTRACT FROM AUTHOR]

Winter survival of organisms has a crucial effect on their fitness in a seasonal environment. We tested whether overwinter survival of male water striders, Aquarius najas (De Geer) (Heteroptera: Gerridae), is associated with the time of season they leave the water for winter diapause. This was performed by comparing parameters of males leaving the water at the beginning of autumn and 1 month later. The results show significantly higher overwinter survival in males of the early diapausing group. They were found to be larger than late diapausing individuals. Overall, overwinter survival was found to be associated with body length. The strength of immune defence measured as encapsulation response against nylon monofilament appeared to be stronger in the early than in the late dia-pausing group. Body length had an effect on the encapsulation rates of water striders, with larger males having a stronger encapsulation response. The amount of lipids was larger in males of the early diapausing group, and the relationship between body length and absolute lipid reserves was positive in both groups. However, a correlation between body reserves and body length was not found when lipid content was expressed as a proportion of total body weight. The results suggest that body length is the main variable linking overwinter survival and resistance against pathogens and parasitoids. This study shows that differences in resistance can explain differential winter survival of larger and smaller A. najas water striders. [ABSTRACT FROM AUTHOR]

Aim To perform a comparative analysis of distribution and genetic diversity in three closely related water strider species ( Gerris) in order to shed light on a putative disjunct distribution in Gerris gillettei. Location Canada and the western United States. Methods Entomological collections from Canada and the United States were surveyed for records of Gerris pingreensis, G. gillettei and Gerris incognitus in order to establish the distribution range of each species. Using samples from present populations, mitochondrial and nuclear DNA sequence variation were used to construct minimum-spanning networks. Distribution patterns and genetic diversity were then compared among species. Results Our results showed that G. incognitus is a genetically distinct species with an unsuspected disjunct distribution. Gerris pingreensis and G. gillettei were found to share genetic polymorphism and they displayed spatial differences only in terms of haplotype distribution, suggesting that they form a single species. Main conclusions Distributional and molecular information uncover unusual distribution patterns and underline taxonomic uncertainty in a group of three closely related Gerris species. Vicariance and failure to recolonize following the last glaciation could explain the G. incognitus disjunction. Morphological and DNA-based species identifications suggest different post-glacial recolonization processes for G. pingreensis and G. gillettei. The putative discontinuous range of G. gillettei may be explained as disjunct phenotypes of a single species. [ABSTRACT FROM AUTHOR]

Water striders (Hemiptera: Gerridae) have been considered as a potential sentinel for mercury (Hg) contamination of freshwater ecosystems, yet little is known about factors that control Hg concentrations in this invertebrate. Striders were collected from 80 streams and rivers in New Brunswick, Canada, in August and September of 2004 through 2007 to assess the influence of factors such as diet, water chemistry, and proximity to point sources on Hg concentrations in this organism. Higher than average Hg concentrations were observed in the southwest and Grand Lake regions of the province, the latter being the location of a coalfired power plant that is a source of Hg (~100 kg annually), with elevated Hg concentrations in the lichen Old Man's Beard (Usnea spp.) in its immediate vicinity. Across all streams, pH and total organic carbon of water were relatively weak predictors of strider Hg concentrations. Female striders that were larger in body size than males had significantly lower Hg concentrations within sites, suggestive of growth dilution. There was no relationship between percent aquatic carbon in the diet and Hg concentrations in striders. For those striders feeding solely on terrestrial carbon, Hg concentrations were higher in animals occupying a higher trophic level. Mercury concentrations were highly variable in striders collected monthly over two growing seasons, suggesting short-term changes in Hg availability. These measurements highlight the importance of considering both deposition and postdepositional processes in assessing Hg bioaccumulation in this species. They also suggest that striders may be more appropriate as a terrestrial rather than an aquatic Hg sentinel, underscoring the importance of understanding the origin of food for organisms used in contaminant studies. [ABSTRACT FROM AUTHOR]

The phenology of three species of Gerroidea (Heteroptera), Metrobates hesperius Uhler (Gerridae), Rhagovelia oriander Parshley (Veliidae), and Rhematobates tenuipesMeinert (Gerridae), was studied on a river in central Illinois (USA).Metrobates hesperius was themost abundant species, and was active from mid-May through mid-October. It was bivoltine and overwintered as eggs.Matinig and oviposition of M. hesperius were observed in mid-July. Rhagovelia oriander was present from mid-May tomid-November. This species was bivoltine (or possibly trivoltine), overwintering as eggs. Rheumatobates tenuipes was not active until early August, and was present to mid-November and was univoltine. It overwinters as adults and possibly as nymphs, and may undergo an extended early season diapause. The three species occupied differing microhabitats and differed in periods of peak abundance, with M. hesperius being most abundant from mid-May through the first of August, and R. tenuipes being most abundant from early August to mid-November. [ABSTRACT FROM AUTHOR]

The wing dimorphic water strider Gerris lacustris L. (Heteroptera: Gerridae) switches to a bivoltine life cycle under favorable climatic conditions. The switch in voltinism is accompanied by a reduction of wing development in the directly reproducing midsummer generation, while the diapausing generation has a high fraction of long-winged individuals. We investigated whether the thermal energy (degree-days) available in natural habitats constrains the combination of developmental pathway and wing morph. Offspring of G. lacustris were reared under quasi-natural conditions at two temperature regimes to determine the thermal constant k required to complete adult development in either wing morph. The thermal constant for egg-to-adult development of the short-winged morph was about 20% lower than of the long-winged morph. Based on the results from the outdoor laboratory experiment, we calculated the total degree-days necessary to complete the possible combinations of wing morph pattern and voltinism. Comparison of these estimates with the thermal energy actually available during the reproductive season of 2004 for various natural habitats (sun-exposed field ponds and shaded forest ponds) suggests that voltinism as well as wing morph pattern is strongly limited by the number of degree-days available in these habitats. On forest ponds, only univoltine life cycles were possible, whereas on field ponds temperature allowed bivoltine life cycles. However, only the eggs laid at the very beginning of the season had the potential to accumulate enough degree-days to complete a bivoltine life cycle with both generations long-winged. We conclude that thermal energy is the main environmental constraint limiting voltinism of populations in the two habitat types. Furthermore, the available thermal energy also seems to influence the determination of the seasonal wing pattern in G. lacustris. [ABSTRACT FROM AUTHOR]

1. Females of the water strider Aquarius paludum insularis (Motschulsky) (Heteroptera: Gerridae) carry males on their backs and oviposit under water after copulation. This study focuses on the benefit A. paludum insularis receives by ovipositing in tandem. 2. Males guarded females in tandem through to the end of oviposition in 85% of copulations. Females in tandem dived deeper than single females, and the density of A. paludum insularis eggs increased with water depth. The proportion of eggs parasitized by a scelionid wasp, Tiphodytes gerriphagus Marchal (Hymenoptera: Scelionidae) decreased with increasing water depth. 3. These results suggest that during oviposition guarding by males is beneficial for females, because it enables pairs to dive and lay eggs deeper and in oviposition sites where the risk of egg parasitism is lower. [ABSTRACT FROM AUTHOR]

In insect wing polymorphism, morphs with fully developed, intermediate, and without wings are recognized. The morphs are interpreted as a trade-off between flight and flightlessness; the benefits of flight are counterbalanced by the costs of development and the maintenance of wings and flight muscles. Such a trade-off has been widely shown for reproductive and developmental parameters, and wing reduction is associated with species of stable habitats. However, in this context, the role of water locomotion performance has not been well explored. We chose seven water striders (Heteroptera: Gerridae) as a model to study this trade-off and its relation to sexual conflicts, namely, Aquarius elongatus (Uhler), Aquarius paludum (Fabr.), Gerris insularis (Motschulsky), Gerris nepalensis Distant, Gerris latiabdominis Miyamoto, Metrocoris histrio (White), and Rhagadotarsus kraepelini Breddin. We estimated the locomotion performance as the legs’ stroke force, measured on tethered specimens placed on water with a force transducer attached to their backs. By dividing force by body weight, we made performance comparisons. We found a positive relationship between weight and force, and a negative one between weight and the force-to-weight ratio among species. The trade-off between water and flight locomotion was manifested as differences in performance in terms of the force/weight ratio. However, the bias toward winged or wing-reduced morphs was species dependent, and presumably related to habitat preference. Water strider species favouring a permanent habitat ( G. nepalensis) showed higher performance in the apterous morph, but in those favouring temporary habitats ( A. paludum and R. kraepelini) morphs’ performance did not differ significantly. Males had higher performance than females in all but three species studied (namely, A. elongatus, G. nepalensis, and R. kraepelini); these three have a type II mating strategy with minimized mating struggle. We hypothesized that in type I mating system, in which males must struggle strongly to subdue the female, males should outperform females to copulate successfully. This was not necessarily true among males of species with type II mating. [ABSTRACT FROM AUTHOR]

We investigated phylogenetic relationships of water striders (Hemiptera-Heteroptera: Gerridae) from the three principal Holarctic genera, Aquarius Schellenberg, Limnoporus Stål and Gerris Fabricius with parsimony analyses of sixty-six morphological characters and DNA sequences from mitochondrial ( cytochrome c oxidase subunit I + II; large mitochondrial ribosomal subunit) and nuclear ( elongation factor 1-alpha) genes. The taxon sampling included all species of Aquarius and Limnoporus, and a dense, near complete, sample of Gerris species with representatives from all subgenera and species groups, and Gigantometra gigas (China) was selected as an outgroup species. A simultaneous analysis of all data sets gave eight equally parsimonious trees, and a strict consensus tree left only a few relationships within Gerris unresolved. While Limnoporus and Gerris each were resolved as monophyletic entities, Aquarius was found to be polyphyletic, because the Nearctic Aquarius remigis-group, comprising A. remigis (Say), A. amplus (Drake and Harris), A. nyctalis (Drake and Hottes) and A. remigoides Gallant and Fairbairn, was placed as sister group to Gerris, while the Andean Aquarius chilensis (Berg) was sister group to all three genera. Remaining species of Aquarius comprised a sister group to the Gerris + the A. remigis-group clade. Based on our phylogenetic reconstruction we discuss relationships within and among the three genera, reassess and diagnose species groups, and discuss zoogeographical relationships among all taxa. [ABSTRACT FROM AUTHOR]

The spatial structure-mediated indirect effects of an aquatic host plant, Trapa japonica (Trapaceae), on survival of a leaf beetle, Galerucella nipponensis (Coleoptera: Chrysomelidae), with regard to predation by a water strider, Gerris nepalensis (Hemiptera: Gerridae), were investigated in an irrigation pond and under indoor conditions. Beetle density, particularly in the first-instar stage of the larvae, became extremely low in the second generation in the pond, even though food resources were abundant. The biological check method, which excludes natural enemies by caging, suggested that a causal factor of the low density was predation by Gerris nepalensis in midsummer and thereafter. Normally growing rosettes extend their leaves horizontally on the water surface. However, some rosettes of T. japonica grew leaves vertically in the later seasons, and such overgrown rosettes were distributed patchily in the ponds. Beetle density was higher on the latter rosettes than on the former ones. The indoor experiment showed that the water strider can feed on the eggs of beetles on normally grown rosettes but not on the overgrown rosettes. Furthermore, female adults of Galerucella nipponensis preferred the overgrown rosettes over the normally grown rosettes for oviposition when water striders were present. These facts suggest that the spatial structure-mediated indirect effects of the host plant modify the interaction between herbivore and predator. [ABSTRACT FROM AUTHOR]

1. We used mtDNA sequence variation to estimate population genetic structure between and among water strider populations of Potamobates williamsi and P . sumaco in the Ecuadorian Amazon. 2. Sequencing of the COI mitochondrial gene revealed 16 haplotypes, which were summarised into four haplotype groups. P . williamsi and P . sumaco shared two common and widespread haplotypes. 3. Population structure was moderate and gene flow was low. Both air and river distances were significantly correlated with gene flow and, thus, indicative of isolation by distance. 4. The genetic structure within and among populations of P. williamsi and P. sumaco was probably not influenced by the dynamic tropical lotic system. [ABSTRACT FROM AUTHOR]

Associations between water-strider species and particular types of vegetation structure result proximately from habitat fidelity at the time of spring colonization and from different preferences for habitats within lakes. Individual gerrids discriminate among lakes during prereproductive dispersal on a trial-and-error basis. Gerrid species differ with respect to preference for emergent cover. Wind and surface disturbance increase preference for sheltered habitats in all species studied but extent of response varies among species. Gerris pingreensis and G. comatus actively seek out emergent cover and open habitats, respectively. G. buenoi is a habitat generalist but distribution of this species is affected by a tendency to avoid other species. Habitat associations of these three common Gerris species are explained in terms of habitat preferences and species interactions. Foraging efficiency varies with habitat structure and species morphology and therefore surface habitats provide a variable selective background for the evolution of gerrid species. [ABSTRACT FROM AUTHOR]

Two species of ocean skaters, Halobates germanus and Halobates micans, live in the tropical and subtropical waters of the Indian Ocean. From December 1992 to December 1993, Halobates was intensively sampled in the easternmost region of the South Indian Ocean (13–18.5°S, 114–121E°), from which there have been a small number of records of Halobates. No H. germanus was caught, but a total of 1190 H. micans were collected, with densities estimated at 13 900–28 100 individuals/km2. This suggests that H. micans lives in the study area at high densities comparable to those in the Atlantic and the Pacific Oceans. We also discuss the possible effects of ocean currents and winds on the geographic distributions of the two Halobates species in the eastern South Indian Ocean. [ABSTRACT FROM AUTHOR]