Respiratory characteristics of the blood pigments of three worms from an intertidal mudflat

Abstract

Three worms living in an intertidal mudflat near Auckland have respiratory pigments with different oxygen-binding properties. The burrowing sipunculid Xenosiphon mundanus has hemerythrin contained within coelomic cells. Oxygen is co-operatively bound to the hemerythrin (Hill's coefficient, n, = 1.8), resulting in a sigmoidal oxygen-binding curve of high oxygen affinity (halfsaturation tension, P₅₀, = 7.0 mm Hg at pH 7.5 and 20°C). Oxygen release is regulated by pH, and the Bohr effect is quantified by Ф = Δ log P₅₀ / ΔpH = - 0.30. The errant polychaete Glycera sp. has hemoglobin-charged coelomocytes with low oxygen affinity (P₅₀ = 13.5 mm Hg at pH 7.3 and 20°C)? and the oxygen-binding curve is essentially hyperbolic and insensitive to pH. The burrowing polychaete Abarenicola affinis has a vascular (circulating) erythrocruorin which binds and releases much oxygen for small changes in PO₂ (Hill's n = 3.8) and is insensitive to pH (Ф = -0.09). The physiological properties of these pigments cannot be related to the availability of oxygen in the near-environment, or to the habits of the animals, but appear to be dictated by the level of body organisation, particularly with regard to the gas exchange surfaces.     

Effects of maternal and embryo characteristics on post-fertilization provisioning in fishes of the genus <Emphasis Type="Italic">Gambusia</Emphasis>

Maternal provisioning of embryos in Gambusia (Poeciliidae) entails both production of large, yolky eggs and mother-to-embryo transfer of nutrients, the latter of which is readily quantified using injection of radiolabeled nutrients. We assayed patterns of nutrient transfer in broods of 26 Gambusia geiseri and 23 Gambusia affinis females, using injection of tritiated leucine. We examined maternal and embryo characteristics affecting the instantaneous rate of transfer and characterized the pattern of transfer to individual embryos within broods. Maternal (female size and condition) and brood characteristics (mean embryo size, developmental stage, brood size) did not predict the mean level of nutrient transfer to embryos in a brood for either species. Within broods, individual provisioning of embryos was not related to developmental stage, but was related to embryo mass in G. affinis with nutrient transfer higher to larger embryos. In addition, overall within-brood variation in nutrient transfer, measured as coefficient of variation in embryo radioactivity, was higher in G. affinis than in G. geiseri.     

Complex interactions between native and invasive fish: the simultaneous effects of multiple negative interactions

We suggest that the ultimate outcome of interactions between native species and invasive species (extinction or coexistence) depends on the number of simultaneous negative interactions (competition and predation), which depends on relative body sizes of the species. Multiple simultaneous interactions may constrain the ability of native species to trade fitness components (i.e., reduced growth for reduced risk of predation) causing a spiral to extinction. We found evidence for five types of interactions between the adults and juveniles of introduced western mosquitofish (Gambusia affinis) and the juveniles of native least chub (Iotichthys phlegethontis). We added ten large (23–28 mm) and seven small (9–13 mm) young-of-the-year (YOY) least chub to replicate enclosures with zero, low, and high densities of mosquitofish in a desert spring ecosystem. Treatments with mosquitofish reduced the average survival of least chub by one-third. No small YOY least chub survived in enclosures with high mosquitofish densities. We also performed two laboratory experiments to determine mortality to predation, aggressiveness, and habitat selection of least chub in the presence of mosquitofish. Mean mortality of least chub due to predation by large mosquitofish was 69.7% over a 3-h trial. Least chub were less aggressive, selected protected habitats (Potamogeton spp.), and were more stationary in the presence of mosquitofish where the dominance hierarchy was large mosquitofish>>large least chubsmall mosquitofish>>small least chub. Least chub juveniles appear to be figuratively caught in a vice. Rapid growth to a size refuge could reduce the risk of predation, but the simultaneous effects of competition decreased least chub growth and prolonged the period when juveniles were vulnerable to mosquitofish predation.     

Impact of introduced native herbivores on a Pistia stratiotes infestation close to the Paraná Delta in Argentina

Pistia stratiotes L. (Araceae) is an important weed in many waterways worldwide. The South American weevil Neohydronomus affinis Hustache (Coleoptera: Curculionidae) and the planthopper Lepidelphax pistiae Remes Lenicov (Hemiptera: Delphacidae) are specific herbivores of P. stratiotes. Both species, plus the oligophagous moth Samea multiplicalis Guenée (Lepidoptera: Crambidae), were released in a P. stratiotes-infested lake in the suburbs of Buenos Aires, Argentina, where previous sampling indicated that specific herbivores were absent. The weevil and the planthopper established and covered the whole lake in under two months. The moth may have also established but its numbers were very low and erratic. Plant cover, biomass per square metre, and individual plant size decreased markedly within a year after the release of the insects. Concomitantly, other floating macrophytes appeared in the lake. Insect abundance was related to mean monthly temperature and light hours, but not the other insect species. However, insect damage levels and the state of the plant population suggest that herbivory was the main factor in lowering the P. stratiotes populations. N. affinis and L. pistiae could be specific, damaging and compatible as biocontrol agents for P. stratiotes.     

Ephemeroptera from Central and South America: New Species of the Farrodes bimaculatus Group with a Key for the Males

The genus Farrodes was recently revised, and two species groups were delimited: Farrodes caribbianus and Farrodes bimaculatus. In that paper the species of the F. caribbianus species group were described or redescribed. In the F. bimaculatus species group eight undescribed species were treated but not described. In the present paper, these new species of the F. bimaculatus species group are described and discussed and a key for the separation of all the species known from male imagines in this group is provided.     

Mosquito oviposition and larvae development in response to kairomones originated by different fish

Predator‐released kairomones indicating the presence of predatory fish are known to alter the behaviour and life‐history traits of several aquatic herbivores. Culex mosquitoes (Diptera: Culicidae) respond to such cues by altering oviposition habitat selection and larval development time. These responses differ among fish species indicating composition differences among fish‐released cues, but the recognition pattern is not clear. This study tested the dependence of fish recognition to co‐evolution and the level of threat to larvae. We compared Culex responses to three fish, the invasive larvivorous Gambusia affinis (Cyprinodontiformes: Poeciliidae), the native larvivorous Aphanius mento (Cyprinodontiformes: Cyprinodontidae) and the native algivorous Garra rufa (Cypriniformes: Cyprinidae). The effects of cues released by the three fish on Culex oviposition and life‐history shifts were compared in field mesocosms and lab tests. Our results showed that ovipositing females were significantly repelled only by cues originated from G. affinis, while developing larvae response was a more general one. Our results support the idea that fish‐released kairomones differ in composition or quantities among different species.     

四川产中菊头蝠喜马拉雅亚种和马铁菊头蝠日本亚种外部形态及头骨的比较

对四川产中菊头蝠喜马拉雅亚种(Rhinolophus affinis himalayanus)和马铁菊头蝠日本亚种(R.ferrumequinum nippon)的23项外部形态指标和22项头骨形态指标进行了测量,并进行数理统计分析。结果表明,(1)中菊头蝠喜马拉雅亚种和马铁菊头蝠日本亚种的23项外部形态测量指标中有2项差异显著(P<0.05),16项差异极显著(P<0.01),其中:中菊头蝠喜马拉雅亚种(n=14)体长小于59 mm(47.30~58.40),尾长小于26 mm(21.69~25.68),耳长小于22 mm(18.36~21.88),前臂长小于56 mm(50.9~54.20),第Ⅲ掌骨第一指节长小于16 mm(13.2~15.53),第Ⅲ掌骨第二指节小于32 mm(27.38~31.74);而马铁菊头蝠日本亚种(n=6)体长大于62 mm(62.43~66.76),尾长大于30 mm(30.56~36.18),耳长大于24 mm(24.47~27.20),前臂长大于56 mm(58.78~63.46),第Ⅲ掌骨第一指节大于19 mm(19.38~21.39),第Ⅲ掌骨第二指节大于34 mm(34.42~38.11),这些差异可作为区分四川产这两个种的依据。(2)中菊头蝠喜马拉雅亚种和马铁菊头蝠日本亚种的22项头骨形态测量指标中,除颅高、听泡间距差异不显著(P>0.05)外,其他20项指标都存在极显著差异(P<0.01)。     

Sexual behaviour of immature male eastern mosquitofish: a way to measure intensity of intra-sexual selection?

Immature males of eastern mosquitofish Gambusia holbrooki start to be sexually active well before their copulatory organ (gonopodium) has completely developed and before they become able to transfer sperm. Sexual activity of males, consisting of copulatory attempts tending to bypass female acceptance, is intense (one attempt per minute) and is likely to be energetically very costly. The sexual behaviour of immature males relative to their maturation stage is described and tested against two possible adaptive explanations. Sexual activity was present in males from the beginning of the development of their gonopodium and increased during the following stages of maturation. Two to three weeks before gonopodium development was completed, sexual activity of immatures was as high as that of adults. Adult males showed aggressive behaviour against a male attempting a copulation, irrespective of the maturity of the latter. Since previous studies have shown that the reproductive success in this species is negatively correlated with male size when male–male competition is low (i.e. when the sex ratio is female biased), but decreases with male size when competition is high, the hypothesis was tested that sexual activity of immature males functions as a way to predict their future reproductive success if they mature at a given size. A second hypothesis tested was that precocious sexual experience improves the efficiency of copulatory attempts. Results were more in agreement with the first hypothesis, since size at maturity of males was influenced by the sex ratio experienced during maturation and precocious experience gave very little advantage.     

The ultrastructure of the eye of the mosquitofishGambusia affinis

Summary The ultrastructure of the tissue components of the eye ofGambusia affinis, excluding the sensory cells, is described. The cornea consists of two different sections of collagenous layers of different density. The choroid includes an argentea composed of- and-melanophores, lipopterinophores and a choriocapillaris associated with the rete mirabile of the choroid body. Bruch's membrane, underlying the retinal pigment layer, can develop complex associations with fibroblasts delimiting the choriocapillaris. The outer section (stroma) of the iris includes several cell types that are not found in the inner or vitread section. In adultGambusia the lens capsule is well developed, but in twoweek-oldSarotherodon larvae the lens epithelium is covered only by a glycocalyx.