Oviposition site choice under conflicting risks demonstrates that aquatic predators drive terrestrial egg-laying

Laying eggs out of water was crucial to the transition to land and has evolved repeatedly in multiple animal phyla. However, testing hypotheses about this transition has been difficult because extant species only breed in one environment. The pantless treefrog, Dendropsophus ebraccatus, makes such tests possible because they lay both aquatic and arboreal eggs. Here, we test the oviposition site choices of D. ebraccatus under conflicting risks of arboreal egg desiccation and aquatic egg predation, thereby estimating the relative importance of each selective agent on reproduction. We also measured discrimination between habitats with and without predators and development of naturally laid aquatic and arboreal eggs. Aquatic embryos in nature developed faster than arboreal embryos, implying no cost to aquatic egg laying. In choice tests, D. ebraccatus avoided habitats with fish, showing that they can detect aquatic egg predators. Most importantly, D. ebraccatus laid most eggs in the water when faced with only desiccation risk, but switched to laying eggs arboreally when desiccation risk and aquatic predators were both present. This provides the first experimental evidence to our knowledge that aquatic predation risk influences non-aquatic oviposition and strongly supports the hypothesis that it was a driver of the evolution of terrestrial reproduction.     

Alternative life cycle strategies of Megalodiscus temperatus in tadpoles and metamorphosed anurans

Megalodiscus temperatus (Stafford, 1905) is a common paramphistome trematode of North American amphibians with a two host life cycle and has been reported to infect frogs and rarely tadpoles. In this study we document the alternative life cycle strategy of M. temperatus in tadpoles and metamorphosed anurans. We show through field work and experimental infections that M. temperatus can establish in both anuran life stages and worms become gravid and release eggs in both tadpoles and metamorphosed frogs. However, worms exhibit differences in route of infection, development, egg production, and diet in tadpoles and metamorphosed anurans. These alternative life history strategies of M. temperatus suggest different selective pressures on the development and reproductive success of these worms in tadpoles and metamorphosed anurans, and we discuss the evolutionary avenues for and constraints on amphibian trematode life cycles presented by these two different anuran life stages.     

Pond tadpoles with generalized morphology: is it time to reconsider their functional roles in aquatic communities?

With rare exceptions, anuran larvae have traditionally been considered to occupy lower trophic levels in aquatic communities where they function as microphagous suspension feeders. This view is being challenged by studies showing that tadpoles with generalized morphology often function as macrophagous predators. Here, we review the literature concerning macrophagy by tadpoles and provide two additional examples involving generalized tadpoles. In the first, we demonstrate with laboratory and field experiments that wood frog (Rana sylvatica) tadpoles are major predators of macroinvertebrates in ponds. In the second, we show that green frog (R. clamitans) tadpoles can cause catastrophic reproductive failure of the wood frog via egg predation. These results and data from other studies challenge the assumption that generalized tadpoles function as filter-feeding omnivores, and question the general applicability of community organization models which assume that predation risk increases with pond permanence. We suggest that predation risk is greater in temporary ponds than in more permanent ponds for many organisms that are vulnerable to predation by tadpoles. This being so, a conditional model based upon interactions that are species-specific, life-stage-specific, and context-dependent may better explain community organization along hydrological gradients than models which assume that temporary ponds have few or no predators. Received: 30 November 1998 / Accepted: 2 May 1999     

Evaluating predation pressure on green treefrog larvae across a habitat gradient

The effect of a predator on the abundance of a prey species depends upon the predators abundance and its ability to capture that prey. The objectives of this research were to evaluate the community structure of predators of green treefrog (Hyla cinerea) tadpoles across habitat types and evaluate the effectiveness of individual predators on H. cinerea tadpoles. Correspondence and cluster analyses of predator frequencies across 23 aquatic habitats indicated that the majority of variance in predator communities was due to a division between permanent and temporary habitats. Experimental work demonstrated that survival of the smallest H. cinerea tadpoles was significantly lower than survival of medium and large tadpoles with the most effective predators, indicating that H. cinerea tadpoles attain a refuge from predation at larger body sizes. We combined the effectiveness of predators in experiments with the abundance of each predator species from the predator community survey to demonstrate that predation pressure on H. cinerea tadpoles is higher in temporary ponds. This pattern may explain in part why this species generally breeds successfully only in permanent habitats. It also confirms that discussions about an increasing gradient of predation pressure from temporary to permanent aquatic habitats should be restricted to individual prey species for which such a gradient has been demonstrated.     

Impacts of eggs and tadpoles of the invasive cane toad (Bufo marinus) on aquatic predators in tropical Australia

Invasive species affect native ecosystems in a variety of ways, and the magnitude of impact may depend upon many factors. In an invading species such as the cane toad (Bufo marinus), the multiphasic life history creates a potential for impact to differ between life history stages. Previous research on the impact of cane toads in Australia has focused on fatal poisoning of predators that ingest terrestrial stages of the toad, but aquatic stages (eggs, larvae) are toxic also. We exposed nine native Australian fish species and one native Australian turtle species to the eggs and larvae of toads. Strong species differences were evident, both in palatability (propensity to attack the egg or larva), and in subsequent responses (e.g. taste and reject the item, vs. ingest it). Toad eggs were less likely than toad tadpoles to be attacked, but also less likely to be rejected before ingestion (probably because the non‐toxic jelly coat masks the presence of toxins in the ovum). As a result, predators were far more likely to be killed by ingesting toad eggs than toad tadpoles. Fortuitously, the spatial and temporal availability of toad egg masses restricts encounter rates with predators, so that overall ecological impact may be low despite the high vulnerability of a fish or turtle that encounters such an egg mass. Understanding such ontogenetic shifts in the nature of interactions and magnitude of impact is crucial if we are to understand the overall ecological impact of invasive species.     

Predator‐induced phenotypic plasticity in an arid‐adapted tropical tadpole

Adaptive phenotypic plasticity is widespread and involves diverse phenotypes. Key environmental stressors, such as predation risk, can simultaneously induce changes in multiple traits, but the magnitude of response is dependent upon the environmental conditions. Species that utilize temporary ponds are expected to exhibit stronger predator‐induced responses in the form of morphology than behaviour (i.e. reduced activity) to meet the demands of rapid development by maintaining high foraging activity while reducing predation risk via morphologically plastic traits. In a laboratory experiment, I examined the effects of predator chemical cues and conspecific alarm cues on activity, development and morphology on Leptodactylus bufonius tadpoles. This species has terrestrial oviposition and completes the early part of its development outside of ephemeral and temporary ponds in the Gran Chaco ecoregion of South America. Tadpoles in the predator treatments exhibited both behavioural and morphological predator‐induced plastic responses. Tadpoles tended to possess shorter, deeper tails when exposed to predators. The greatest reduction in activity was observed in tadpoles exposed to both predator and conspecific alarm cues, which subsequently resulted in the slowest development. Temporary and ephemeral pond adapted species with terrestrial oviposition may capitalize on a head start in development by being able to afford reduced growth rates via a reduction in activity. This may occur when the constraints imposed by pond hydroperiod (e.g. risk of pond drying) are relaxed when compared with species with aquatic oviposition, which must undergo all stages of development during the pond's hydroperiod. Thus, in addition to the predator and hydroperiod gradients, examining phenotypically plastic responses along a ‘terrestriality gradient’ in a comparative framework would provide insights as to the costs and benefits of increasing terrestriality in anuran reproductive modes to environmental stressors.     

Better desiccated than eaten by fish: Distribution of anurans among habitats with different risks to offspring

1. Freshwater species with complex life cycles face a trade-off between the risks of offspring mortality due to desiccation in temporary habitats and due to predators common in long-duration habitats, especially fish. In real-world conditions, intermediate-gradient areas that are highly suitable for some ecological specialists are often limited. I examined the relative significance of drivers of the permanence–predation gradient in habitat selection by pond-breeding anurans.
2. Anuran oviposition was investigated at the community level in fish pond landscapes with only three types of habitat, permanent fish-containing ponds and highly desiccation-prone pools, either fishless or recently emptied of fish and with fish odour (fish cue). Altogether, 65 ponds/pools, interspersed in four clusters, were examined for the presence of egg masses.
3. Bufo bufo was the only species preferring permanent ponds. Egg masses of Rana sp. (Rana arvalis/Rana temporaria) occurred in all fishless pools, and less frequently in the ponds. Bufotes viridis and long larval period species Pelobates fuscus and Hyla orientalis oviposited almost exclusively in fishless pools. Fish-cue pools were avoided by all species. Anuran richness was higher in fishless pools than in permanent ponds. Species distribution between the two habitats was nested, with both common and rare species occurring in fishless pools.
4. The results indicate the primacy of offspring predation risk over hydroperiod constraints in oviposition decision-making by fish-intolerant anurans. The absence of some species from ponds and pools with fish or fish cues shows that non-consumptive interactions may better explain the scarcity of anuran larvae in waters dominated by fish than actual consumption. The strict avoidance of fish habitats despite their proximity to fishless patches indicates fine-scale assessment of predation risk. However, rigid habitat selection against fish predation on offspring may prove maladaptive if habitats with high desiccation risk are the main alternative and are indiscriminately preferred. Maintenance of fishless wetlands with a hydroperiod sufficient to allow completion of metamorphosis should be a conservation priority for anuran diversity in areas where fishless habitats are limited.

     

Wasp predation and wasp-induced hatching of red-eyed treefrog eggs

Eggs often suffer high levels of predation and, compared with older animals, embryos have few options available for antipredator defence. None the less, hatchlings can escape from many predators to which eggs are vulnerable. I studied early hatching as an antipredator defence of red-eyed treefrog embryos, Agalychnis callidryas, in response to egg predation by social wasps (Polybia rejecta). Red-eyed treefrogs attach their eggs to vegetation overhanging water, where they are exposed to arboreal and aerial predators. Wasps attacked half the egg clutches and killed almost a quarter of the eggs I monitored at a natural breeding site in Panama. Hatching tadpoles fall into the water, where they face aquatic predators. As predicted from improved survival of older hatchlings with aquatic predators, most undisturbed eggs hatched relatively late. However, many younger embryos directly attacked by wasps hatched immediately. Embryos attacked by wasps hatched as much as a third younger than the peak undisturbed hatching age, and most hatching embryos escaped. Thus hatching is an effective defence against wasp predation, and plasticity in hatching stage allows embryos to balance risks from stage-specific egg and larval predators. Wasp-induced hatching is behaviourally similar to the snake-induced hatching previously described in A. callidryas, but occurs in fewer eggs at a time, congruent with the scale of the risk. Individual embryos hatch in response to wasps, which take single eggs, whereas whole clutches hatch in response to snakes, which consume entire clutches. Embryos of A. callidryas thus respond appropriately to graded variation in mortality risks. Copyright 2000 The Association for the Study of Animal Behaviour.     

Effects of Predation by Invasive Western Mosquitofish(Gambusia affinis) on Survival of Eggs,Embryos and Tadpoles of Pelophylax nigromaculatus and Duttaphrynus melanostictus in South China

Alien species are one of the most serious threats to the decline and extinction of native amphibian populations. In this study, we examined the predation of invasive Western Mosquitofish Gambusia affinis on the eggs, embryos, and tadpoles of Duttaphrynus melanostictus and Pelophylax nigromaculatus in south China. Our results suggested that the survival of eggs and embryos remaining in the egg capsules of P. nigromaculatus and D. melanostictus was significantly higher than those removed from the egg capsule at 12-h intervals within 72 h in the presence of G. affinis. The survival of P. nigromaculatus eggs and embryos without egg capsules was significantly lower than those of D. melanostictus without egg capsules. The survival of P. nigromaculatus eggs and embryos with egg capsules was significantly higher than those of D. melanostictus with egg capsules from 24 h to 72 h except for 12 h. The survival of D. melanostictus tadpoles was significantly higher than that of P. nigromaculatus tadpoles in the presence of G. affinis. The survival of Gosner stage 26 tadpoles of P. nigromaculatus was significantly higher than that of Gosner stage 30 tadpoles from 12 h to 60 h, but there were no significant differences at 72 h. In contrast, the survival of Gosner stage 26 tadpoles of D. melanostictus was significantly lower than that of Gosner stage 30 tadpoles within 72 h, recording every 12 h. The increasing temperature caused a significant increase in predation by G. affinis on P. nigromaculatus eggs and embryos. The outer jelly capsule surrounding anurans eggs might serve as a mechanical defense against predation by G. affinis due to its large diameter, relatively stationary state and unpalatability. The differences in the vulnerability of P. nigromaculatus and D. melanostictus embryos and tadpoles to G. affinis probably due to differences in the unpalatability, black skin and activity. Based on the magnitude of predation by G. affinis on the eggs, embryos and tadpoles of these two species and the combined impact of temperature, we might speculate that invasive G. affinis and global warming would have more detrimental impacts on population viability of P. nigromaculatus than D. melanostictus in China.     

PHYLOGENETIC ANALYSES REVEAL UNEXPECTED PATTERNS IN THE EVOLUTION OF REPRODUCTIVE MODES IN FROGS

Understanding phenotypic diversity requires not only identification of selective factors that favor origins of derived states, but also factors that favor retention of primitive states. Anurans (frogs and toads) exhibit a remarkable diversity of reproductive modes that is unique among terrestrial vertebrates. Here, we analyze the evolution of these modes, using comparative methods on a phylogeny and matched life‐history database of 720 species, including most families and modes. As expected, modes with terrestrial eggs and aquatic larvae often precede direct development (terrestrial egg, no tadpole stage), but surprisingly, direct development evolves directly from aquatic breeding nearly as often. Modes with primitive exotrophic larvae (feeding outside the egg) frequently give rise to direct developers, whereas those with nonfeeding larvae (endotrophic) do not. Similarly, modes with eggs and larvae placed in locations protected from aquatic predators evolve frequently but rarely give rise to direct developers. Thus, frogs frequently bypass many seemingly intermediate stages in the evolution of direct development. We also find significant associations between terrestrial reproduction and reduced clutch size, larger egg size, reduced adult size, parental care, and occurrence in wetter and warmer regions. These associations may help explain the widespread retention of aquatic eggs and larvae, and the overall diversity of anuran reproductive modes.     

The advantage of no defense: predation enhances cohort survival in a desert amphibian

The impacts that predators have on prey behavior, growth, survival, and ultimately the composition of many ecological communities are mediated by prey defenses and the susceptibility of prey to predators. We hypothesized that prey populations inhabiting short-lived, species-poor, aquatic environments should lack significant morphological, developmental, and behavioral responses to predators and are therefore highly susceptible to predation. Furthermore, we predicted that the resultant decrease in prey density and increase in per capita resources due to high susceptibility to predators should enhance overall cohort survival because of enhanced growth of surviving prey. To test these ideas, we performed laboratory and outdoor mesocosm experiments to disentangle multiple effects of predators on an anuran (Scaphiopus couchii); a species highly adapted to breeding in ephemeral habitats and that has one of the shortest larval periods of all anurans. Chemical (presence of predator) and lethal predator cues (predator plus consumed conspecific) elicited no response in behavior, development, or morphology, indicating a lack of defensive mechanisms. Survivorship was significantly reduced in treatments where tadpoles were exposed to predators. However, this reduction in prey density led to accelerated time to metamorphosis, conferring an advantage to survivors who must metamorphose before ephemeral ponds dry. Our experiments demonstrated that in short-lived environments, prey may exhibit little or no response to the presence of predators presumably because selection for anti-predator defenses is countered by selection for rapid metamorphosis. However, predation actually resulted in an increase in overall cohort survival. Although predators are relatively rare in highly ephemeral aquatic environments, they may play an important role in facilitating the long-term persistence of their prey by reducing prey density.     

Far from home: responses of an American predator species to an American prey species in a jointly invaded area of Australia

Far from their native ranges in the Americas, two invasive species come into contact in Australian waterbodies. Cane toads (Rhinella marina) fatally poison many anurophagous predators, whereas eastern mosquito fish (Gambusia holbrooki) voraciously consume anuran larvae. As cane toads spread south along Australia’s east coast, they are colonizing areas where mosquito fish are abundant. What happens when these two American invaders encounter each other in Australia? We tested the responses to toad tadpoles of mosquito fish from populations that were sympatric versus allopatric with cane toads. Toad-sympatric fish generally ignored toad tadpoles. Toad-allopatric fish initially consumed a few tadpoles, but rapidly developed an aversion to these toxic prey items. The laboratory-reared progeny of toad-allopatric fishes were more likely to approach toad tadpoles than were the offspring of toad-sympatric fishes, but the two groups learned toad-avoidance at similar rates. Thus, mosquito fish show an innate aversion to cane toad tadpoles (perhaps reflecting coevolution with North American bufonid taxa), as well as an ability to rapidly learn taste-aversion. Our comparisons among populations suggest that several decades of toad-free existence in Australia caused a decline in the fishes’ innate (heritable) aversion to toads, but did not affect the fishes’ capacity to learn toad-avoidance after an initial exposure. Any impact of mosquito fish on cane toads thus is likely to be transitory. The rapid (<100-year) time frame of these shifts (the initial weakening of the fishes’ response during toad-allopatry, and its recovery after secondary contact) emphasizes the dynamic nature of faunal responses during biological invasions, and the interplay between adaptation and phenotypic plasticity.     

Indirect ecological impacts of an invasive toad on predator–prey interactions among native species

One of the many ways that invasive species can affect native ecosystems is by modifying the behavioural and ecological interactions among native species. For example, the arrival of the highly toxic cane toad (Bufo marinus) in tropical Australia has induced toad-aversion in some native predators. Has that shift also affected the predators’ responses to native prey—for example, by reducing vulnerability of native tadpoles via a mimicry effect, or increasing vulnerability of other prey types (such as insects) via a shift in predator feeding tactics? We exposed a native predator (northern trout gudgeon, Mogurnda mogurnda) to toad tadpoles in the laboratory, and measured effects of that exposure on the fish’s subsequent intake of native tadpoles and crickets. As predicted, toad-exposed fishes reduced their rate of predation on (palatable) tadpoles of native frogs (Litoria caerulea and L. nasuta). If alternative prey (crickets) were available also, the toad-exposed fishes shifted even more strongly away from predation on native tadpoles. Thus, invasion of a toxic species can provide a mimicry benefit to native taxa that resemble the invader, and can shift predation pressure onto other taxa.     

Choice of optimal oviposition sites by Hoplobatrachus occipitalis (Anura: Ranidae) in an unpredictable and patchy environment

 The rock pools on the river bank of the Comoé National Park (West Africa) provide a very diverse and unpredictable environment for anuran larval development. Because rock pools differ considerably in biotic and abiotic parameters, it should be adaptive for reproducing anurans to choose the most suitable oviposition sites. During the beginning of each rainy season (March to May), from 1991 to 1995, we investigated the allocation of breeding sites by Hoplobatrachus occipitalis, counted the number of eggs, and measured several biotic and abiotic factors that might influence the choice of a spawning site. The probability of predation by conspecific cannibalistic tadpoles and the water-holding capacity (WHC) of pools were the best predictor of number of eggs laid. We experimentally investigated the influence of these two parameters on egg-laying and showed that adults potentially can assess the presence, density, and size of tadpoles in pools by chemical cues. Likewise, manipulation of the water-holding capacity caused a rapid change in egg-laying behavior. To assess the risk of desiccation, frogs have to visit familiar pools repeatedly to monitor the decrease in volume over time and thus gain information about the pools’ water-holding capacity. Received: 22 April 1996 / Accepted: 17 July 1996     

Direct and indirect effects of the introduced toad Bufo marinus (Anura: Bufonidae) on populations of native anuran larvae in Australia

Introduced species are frequently believed to have adverse effects on native biota and ecosystems. However, much of our knowledge of the ecological impacts of introduced species is anecdotal, and the mechanisms controlling these effects are often poorly understood. I used replicated artificial pond experiments to investigate the impact of eggs and hatchlings of the introduced toad Bufo marinus on populations of native anuran larvae (Limnodynastes ornatus and Litoria rubella) in Australia. Bufo marinus eggs and hatchlings are highly toxic to predatory native tadpoles. Under naturalistic conditions, populations of predatory L. ornatus tadpoles experienced significantly reduced survival when exposed to Bufo eggs and hatchlings. The impact of Bufo on L. ornatus survival was positively correlated with Bufo density. However, the toxic effects of Bufo on L. ornatus indirectly facilitated the survival of later-breeding L. rubella by altering predator-prey interactions between L. ornatus and L. rubella. Limnodynastes ornatus tadpoles are voracious predators of L. rubella eggs and hatchlings. Consequently, the negative impact of Bufo on populations of L. ornatus tadpoles reduced the intensity of predation by L. ornatus tadpoles on L. rubella eggs and hatchlings, thereby increasing L. rubella survival. The results demonstrate that B. marinus plays an important role in structuring native larval anuran communities via direct and indirect mechanisms, and that Bufo may have both negative and positive effects on populations of native anuran larvae. As far as I am aware, these are the first quantitative data to demonstrate that introduced fauna may affect populations of native biota via toxic effects.     

Environmental variables associated with the distribution and occupancy of habitat specialist tadpoles in naturally acidic,oligotrophic waterbodies

Environmental factors play an integral role, either directly or indirectly, in structuring faunal assemblages. Water chemistry, predation, hydroperiod and competition influence tadpole assemblages within waterbodies. We surveyed aquatic predators, habitat refugia, water height and water chemistry variables (pH, salinity and turbidity) at 37 waterbodies over an intensive 22‐day field survey to determine which environmental factors influence the relative abundance and occupancy of two habitat specialist anuran tadpole species in naturally acidic, oligotrophic waterbodies within eastern Australian wallum communities. The majority of tadpoles found were of Litoria olongburensis (wallum sedge frog) and Crinia tinnula (wallum froglet) species, both habitat specialists that are associated with wallum waterbodies and listed as Vulnerable under the IUCN Red List. Tadpoles of two other species (Litoria fallax (eastern sedge frog), and Litoria cooloolensis (cooloola sedge frog)) were recorded from two waterbodies. Tadpoles of Litoria gracilenta (graceful treefrog) were recorded from one waterbody. Relative abundance and occupancy of L. olongburensis tadpoles were associated with pH and water depth. Additionally, L. olongburensis tadpole relative abundance was negatively associated with turbidity. Waterbody occupancy by C. tinnula tadpoles was negatively associated with predatory fish and water depth and positively associated with turbidity. Variables associated with relative abundance of C. tinnula tadpoles were inconclusive and further survey work is required to identify these environmental factors. Our results show that the ecology of specialist and non‐specialist tadpole species associated with ‘unique’ (e.g. wallum) waterbodies is complex and species specific, with specialist species likely dominating unique habitats.     

Within‐patch oviposition site shifts by spider mites in response to prior predation risks decrease predator patch exploitation

In egg‐laying animals with no post‐oviposition parental care, between‐ or within‐patch oviposition site selection can determine offspring survival. However, despite the accumulation of evidence supporting the substantial impact predators have on oviposition site selection, few studies have examined whether oviposition site shift within patches (“micro‐oviposition shift”) reduces predation risk to offspring. The benefits of prey micro‐oviposition shift are underestimated in environments where predators cannot disperse from prey patches. In this study, we examined micro‐oviposition shift by the herbivorous mite Tetranychus kanzawai in response to the predatory mite, Neoseiulus womersleyi, by testing its effects on predator patch exploitation in situations where predatory mites were free to disperse from prey patches. Adult T. kanzawai females construct three‐dimensional webs on leaf surfaces and usually lay eggs under the webs; however, females that have experienced predation risks, shift oviposition sites onto the webs even in the absence of current predation risks. We compared the predation of eggs on webs deposited by predator‐experienced females with those on leaf surfaces. Predatory mites left prey patches with more eggs unpredated when higher proportions of prey eggs were located on webs, and egg survival on webs was much higher than that on leaf surfaces. These results indicate that a micro‐oviposition shift by predator‐experienced T. kanzawai protects offspring from predation, suggesting adaptive learning and subsociality in this species. Conversely, fecundity and longevity of predator‐experienced T. kanzawai females were not reduced compared to those of predator‐naïve females; we could not detect any costs associated with the learned micro‐oviposition shift. Moreover, the previously experienced predation risks did not promote between‐patch dispersal of T. kanzawai females against subsequently encountered predators. Based on these results, the relationships of between‐patch oviposition site selection and micro‐oviposition shift are discussed.     

我国蝌蚪的科级分类研究

2017年末,我国的两栖动物已记录3目14科466种,其中,无尾目Anura 10科386种。蝌蚪是无尾两栖类物种的幼体,具有一系列适应水生生活的形态特征和一个特别的变态过程,是无尾目的主要标志之一。我国蝌蚪的形态特征散见于各个物种的形态描述,而对蝌蚪科级分类的系统研究却阙如。本文基于蝌蚪的8个形态学分类性状,概述了我国除亚洲角蛙科Ceratobatrachidae外9个科(铃蟾科Bombinatoridae、角蟾科Megophryidae、蟾蜍科Bufonidae、雨蛙科Hylidae、蛙科Ranidae、叉舌蛙科Dicroglossidae、浮蛙科Occidozygidae、树蛙科Rhacophoridae、姬蛙科Microhylidae)的蝌蚪分类特征,系统阐述了蝌蚪科级分类特征的分类和适应意义。     

水蛭捕食两栖类卵

许多卵生动物具有对付食卵者的精巧策略以降低死亡率,因为早期发育阶段的捕食压力能显著影响具复杂生活史动物的生存。两栖动物卵被水蛭等很多物种所捕食。我们查阅了水蛭捕食两栖类卵的文献,发现27篇论文。在所报道的水蛭捕食两栖类卵的例子中,无尾类(3.6%,n=591)明显多于有尾类(1.6%,n=255)。此外,我们第一次记录到水蛭捕食四趾螈(Salamandrina perspicillata)卵,这也是西欧有尾类的第一例报道。我们没有发现两个两栖动物类群间存在差异。然而,当我们分别分析来自北美、欧洲和亚洲三个地区的数据时,发现北美的有尾类和无尾类间存在显著差异。水蛭可捕食各生活史阶段的两栖动物,因此,水蛭应归为一些两栖类的天敌。     

The evolution of reproductive diversity in Afrobatrachia: A phylogenetic comparative analysis of an extensive radiation of African frogs

The reproductive modes of anurans (frogs and toads) are the most diverse of terrestrial vertebrates, and a major challenge is identifying selective factors that promote the evolution or retention of reproductive modes across clades. Terrestrialized anuran breeding strategies have evolved repeatedly from the plesiomorphic fully aquatic reproductive mode, a process thought to occur through intermediate reproductive stages. Several selective forces have been proposed for the evolution of terrestrialized reproductive traits, but factors such as water systems and co‐evolution with ecomorphologies have not been investigated. We examined these topics in a comparative phylogenetic framework using Afrobatrachian frogs, an ecologically and reproductively diverse clade representing more than half of the total frog diversity found in Africa (～400 species). We infer direct development has evolved twice independently from terrestrialized reproductive modes involving subterranean or terrestrial oviposition, supporting evolution through intermediate stages. We also detect associations between specific ecomorphologies and oviposition sites, and demonstrate arboreal species exhibit an overall shift toward using lentic water systems for breeding. These results indicate that changes in microhabitat use associated with ecomorphology, which allow access to novel sites for reproductive behavior, oviposition, or larval development, may also promote reproductive mode diversity in anurans.