Multi‐scale oviposition site selection in two mosquito species

1. In organisms characterised by complex life cycles, habitat selection often occurs at multiple spatial scales. For instance, female mosquitoes searching for an appropriate aquatic habitat to oviposit their eggs should also consider the characteristics of the terrestrial landscape in which it is embedded. 2. In this study, a field experiment was conducted to test for multi‐scale oviposition site selection in two mosquito species. Artificial pools were placed in two adjacent landscapes, olive plantations and a citrus orchard, mainly differing in their blooming periods and nectar availability. Pools were organised in three pairs: predatory caged fish were present in both pools, in one pool, or in none. 3. Early during the season, most of the egg rafts were laid by Culiseta longiareolata females in pools located within the blooming citrus orchard. When blooming shifted to the olive plantation, C. longiareolata become opportunistic. Culex pipiens females appeared later on during the season, when egg rafts of C. longiareolata were scarce, and they exhibited a higher selectivity to the olive plantation, although its blooming ended. In addition, the selectivity of C. pipiens to fish‐free pools was stronger than that of C. longiareolata. 4. Culex pipiens was more selective, possibly due to its high dispersal ability, which can lower movement cost and enhance the ability to gather environmental information. A trade‐off among gonotrophic cycles, combined with a shorter breeding season and limited recognition ability of the predatory fish may have reduced C. longiareolata selectivity. These differential oviposition patterns can strongly affect the population and community dynamics of both species.     

Defining core habitat of local populations of the gray treefrog (Hyla versicolor) based on choice of oviposition site

Concern over amphibian population declines and loss of terrestrial and aquatic habitat have emphasized the need to define habitat requirements for each stage in a species' life history. The realization that pond-breeding amphibians spend most of their lives in the terrestrial environment suggests the need to protect terrestrial as well as aquatic habitat. Many studies on amphibian populations have focused on emigration from breeding sites to define habitat use; however these studies do not typically elucidate terrestrial activities of adults within the breeding season. We measured colonization rates of artificial pools by gray treefrogs (Hyla versicolor) at multiple distances from natural breeding ponds. We found a non-random distribution of egg deposition among distances, with 95% of eggs deposited within 15 m of the breeding pond. Additionally, we found that the time to first colonization of artificial pools increased with respect to distance. Our results indicate that adult gray treefrogs may travel up to 200 m within a breeding season, and that multiple breeding ponds may be considered part of a single population. We suggest that a minimum core terrestrial habitat of 60 m surrounding breeding sites is appropriate for protection of local populations of gray treefrogs.     

Functional heterogeneity of dry-season fish refugia across a Mediterranean catchment: the role of habitat and predation

SUMMARY 1. Fish in Mediterranean streams survive through the summer in residual surface waters, encompassing a broad range of abiotic and biotic conditions. Yet, the extent to which fish assemblages may be shaped by functional heterogeneity in dry-season refugia is largely unknown. This study addresses this issue, by examining fish assemblage and population attributes, and predation patterns in residual summer habitats (12 pools and six runs) across a Mediterranean catchment in south-west Portugal.
2. Species richness was fairly constant among runs but increased with pool size, with the addition of exotics and rare natives to large pools resulting in nested subsets. The four most common species (chub, nase, loach and eel) were considered generalists in terms of their use of dry-season refugia. Conversely, rare species presented more specialised habitats, with barbel and exotics favouring pools and stickleback favouring runs.
3. Age and size of the two most common species varied among dry-season habitats. Age 0 chub were restricted to runs, where spawning stages (age 2 and older fish) were also more represented. Age 0 nase also concentrated in runs, but the individuals collected in pools exhibited greater growth. Conversely, age 2 and older nase were proportionally more abundant in pools, but with greater growth and better condition in runs.
4. The otter was the main fish predator, consuming fish of all species and size classes, irrespective of habitat. Otter activity concentrated in pools, where predation risk for cyprinids seemed to be much higher than in runs.
5. Dry-season refugia apparently vary in functional importance for different fish species and life stages, acting as complementary units in the landscape. Therefore, the presence of both pool and run refugia trough the summer dry season may play a critical role in promoting the persistence of native species in Mediterranean streams.     

Life on the edge: the demography of short-season populations of deer mice

We documented populations of deer mice in the Kananaskis Valley, southwestern Alberta, Canada from 1979 to 1997 to determine whether these short-season populations were more, or less, variable than populations in more temperate environments. We then examined patterns of reproduction, age-specific survival, and immigration to explain variation in summer population growth. Population densities showed no multi-annual periodicity and were generally low. At maximum, numbers doubled over the breeding season, but declined over the breeding season in 4 of 16 yr. Variability in population density was low, and similar to that of Peromyscus populations in more temperate environments. No demographic parameters were related to spring population densities, and immigration rates were low when conditions for survival of nestlings and adults were favorable. Variation in summer population growth was attributed primarily to variation in nestling survival among years.     

Factors Associated with the Seasonal Variation in the Incidence of Pituitary Cysts in Nine-Spined Sticklebacks,Pungitius pungitius L.

Cysts among the prolactin cells in the pituitary gland of the nine-spined stickleback, Pungitius pungitius L., are most common during and shortly after periods of high mortality that mark the end of the reproductive season. Fish are oldest at this time of year. Nevertheless, cysts may occur in breeding as well as spent fish, and their presence does not relate to changes in oocyte development. They can be induced by starving animals in February, but not in September—October. Starved fish always have small prolactin cells and nuclei. It is suggested that cysts form in older fish in response to stress, be this natural or induced. No correlation was noticed between the condition factor of fish caught in the wild, and the incidence of pituitary cysts.     

Annual variation in long‐distance dispersal driven by breeding and non‐breeding season climatic conditions in a migratory bird

Long‐distance dispersal is a fundamental process in ecology and evolution but the factors that influence these movements remain poorly understood in most species. We used stable hydrogen isotopes to quantify the rate and direction of long‐distance immigration in a breeding population of American redstarts and to test whether the settlement decisions that result in long‐distance dispersal are driven by habitat saturation or by the phenology of breeding‐season resources. Our results provide evidence that both natal dispersal and breeding dispersal were influenced by the timing of breeding‐season phenology, with both age classes more likely to disperse north in years when the onset of breeding‐season phenology occurs earlier than normal. Yearlings were also more likely to disperse north following winters with poor habitat quality on their non‐breeding grounds, demonstrating that carry‐over effects from the non‐breeding season influence natal dispersal in this species. Collectively, these results are consistent with the hypothesis that American redstarts use the phenology of breeding season resources as a cue to select breeding sites. Our results suggest that long‐distance dispersal may allow individuals to rapidly respond to advancing phenology caused by global climate change, though their ability to do so may be constrained by long‐term decline in habitat quality predicted for their tropical non‐breeding grounds.     

Reproductive effort and efficiency in the female common goby, Pomatoschistus microps (Krøyer) (Teleostei: Gobioidei)

Reproductive effort and efficiency are terms which together help to describe the reproductive investment of spawning fish. In this paper they are applied to a small and abundant inshore fish, the common goby, Pomatoschistus microps (Kroyer), based on data collected from the wild, and by modelling likely breeding patterns. Wet calorimetry was used to determine the energy content offish tissue, and this allowed reproductive effort to be expressed as both an energy and a weight ratio of gonad to somatic body. The gonadosomatic index (GSI) calculated as an energy ratio was greater than that calculated as a dry "weight ratio". For ripe females the GSI (dry weight) at the onset of breeding was 67.5%. Theoretical and observed values of the maximum number of egg batches laid by a single female during a 16-week breeding season are 9-10, and this corresponds to a total caloric investment of almost 12 kJ. Estimates of the reproductive efficiency, using the dietary energy content during the breeding season, range from 28.2% to a maximum of 44.0%. These values are among the highest calculated for a fish species, and are in keeping with the long and intensive breeding strategy observed in the wild population.     

Culex mosquitoes in temporary urban rain pools: seasonal dynamics and relation to environmental variables.

The study was conducted in a park of Buenos Aires City, where a total of 89 rain pools were sampled weekly for mosquito immature stages over a one-year period. The aim of the present paper was to investigate the seasonal dynamics of three Culex species breeding in temporary rain pools and to analyze the relationships of the presence of these species to pool dimensions, pool age, vegetation, and insolation degree. The three species showed differences in their seasonal patterns, Culex dolosus being present during the whole year, Culex pipiens mainly in the summer season, and Culex maxi almost exclusively during the fall. The variable explaining most of the variation among sampling dates in species composition was weekly mean temperature. A significant positive association was detected among mosquito species, as they were recorded together more frequently than expected by chance. The statistical analyses performed revealed significant positive relationships of all three mosquito species to increasing surface area, whereas no relationship to insolation degree was detected in the studied pools. Culex pipiens and Culex dolosus showed positive relationships to increasing vegetation cover, whereas the presence of Culex dolosus was also related to pool age.     

BEHAVIORAL EVIDENCE OF THERMAL STRESS FROM OVERHEATING IN UK BREEDING GRAY SEALS

Gray seals ( Halichoerus grypus ) in the UK exhibit clear preferences for pupping close to pools of water on inland breeding sites. The reasons for this are unclear as seals are thought to derive all their water requirements from the metabolism of fat. Likewise, the prospect of seals overheating during the UK's cool, damp, autumnal breeding seasons, has seemed unlikely, but has not been previously explored. Here, we provide preliminary behavioral evidence of thermal stress in female gray seals breeding on the island of North Rona, Scotland. Video footage provided measures of proximity to, and the proportion of animals bathing in, pools in relation to meteorological data (temperature, mean sea-level pressure, rainfall, wind speed and direction) on four dates spread through a single breeding season. The proportion of females close to pools increased with pressure (warmer, drier conditions) and decreased on wetter days. In addition, analyses of colony-wide patterns of seal dispersion showed that females tended to be closer to pools of water at higher pressures and temperatures and at lower wind-speeds. These results provide the first evidence of thermal stress and behavioral thermoregulation through access to pools of water in a phocid breeding in temperate autumnal conditions.     

Intraseasonal patterns in shorebird nest survival are related to nest age and defence behaviour

Nest survival may vary throughout the breeding season for many bird species, and the nature of this temporal variation can reveal the links between birds, their predators, and other components of the ecosystem. We used program Mark to model patterns in nest survival within the breeding season for shorebirds nesting on arctic tundra. From 2000 to 2007, we monitored 521 nests of five shorebird species and found strong evidence for variation in nest survival within a nesting season. Daily nest survival was lowest in the mid-season in 5 of 8 years, but the timing and magnitude of the lows varied. We found no evidence that this quadratic time effect was driven by seasonal changes in weather or the abundance of predators. Contrary to our prediction, the risk of predation was not greatest when the number of active shorebird nests was highest. Although nest abundance reached a maximum near the middle of the breeding season, a daily index of shorebird nest activity was not supported as a predictor of nest survival in the models. Predators’ access to other diet items, in addition to shorebird nests, may instead determine the temporal patterns of nest predation. Nest survival also displayed a positive, linear relationship with nest age; however, this effect was most pronounced among species with biparental incubation. Among biparental species, parents defended older nests with greater intensity. We did not detect a similar relationship among uniparental species, and conclude that the stronger relationship between nest age and both nest defence and nest survival for biparental species reflects that their nest defence is more effective.     

Seasonal pattern of filial cannibalism by Apogon doederleini mouthbrooding males

In temperate waters of southern Japan, mouthbrooding males of the cardinal fish Apogon doederleini sometimes ate their entire brood within a day of spawning. In spite of annual variation in age structure and length of the breeding season, however, the annual cannibalism rate (broods cannibalized to total broods spawned) was nearly constant, 12–16%. Fish 1 year old frequently cannibalized early broods of the season, especially the first brood, whereas the cannibalism rate by 2 year-old fish did not vary within the season. In contrast, the cannibalism by older males increased late in the season. This tendency was attributed to their different allocation patterns to growth and reproduction. For 1 year-old fish, which can enhance future reproductive success by growth and cannibalizing on early broods instead of mouthbrooding (at relatively low temperatures), this may be a tactic for investing energy in growth. For fish 3 years, which have more breeding cycles and grow little, cannibalizing late broods may be energetic compensation for their poor somatic condition. No seasonal variation of cannibalism by 2 year-old fish can be explained by their intermediate nature of growth and reproduction. Multiple mate availability is one factor facilitating the cannibalism by 2 and 3 + year-old fish whose operational sex ratio is female-biased.     

Temporal changes in replicated experimental stream fish assemblages: predictable or not?

Summary 1. Natural aquatic communities or habitats cannot be fully replicated in the wild, so little is known about how initially identical communities might change over time, or the extent to which observed changes in community structure are caused by internal factors (such as interspecific interactions or traits of individual species) versus factors external to the local community (such as abiotic disturbances or invasions of new species).
2. We quantified changes in seven initially identical fish assemblages, in habitats that were as similar as possible, in seminatural artificial streams in a 388-day trial (May 1998 to May 1999), and compared the change to that in fish assemblages in small pools of a natural stream during a year. The experimental design excluded floods, droughts, immigration or emigration. The experimental fish communities diverged significantly in composition and exhibited dissimilar trajectories in multivariate species space. Divergence among the assemblages increased from May through August, but not thereafter.
3. Differences among the experimental assemblages were influenced by differences that developed during the year in algae cover and in potential predation (due to differential survival of sunfish among units).
4. In the natural stream, fish assemblages in small pools changed more than those in the experimental units, suggesting that in natural assemblages external factors exacerbated temporal variation.
5. Our finding that initially identical assemblages, isolated from most external factors, would diverge in the structure of fish assemblages over time suggests a lack of strong internal, deterministic controls in the assemblages, and that idiosyncratic or stochastic components (chance encounters among species; vagaries in changes in the local habitat) even within habitat patches can play an important role in assemblage structure in natural systems.     

Investment in testes,sperm‐duct glands and lipid reserves differs between male morphs but not between early and late breeding season in Pomatoschistus minutus

This study of the sand goby Pomatoschistus minutus, a nest‐holding fish with paternal care, focused on gonadal investment among males of different sizes collected early and late in the breeding season. All males caught at the nest had breeding colour, whereas trawl‐caught fish consisted of males both with and without colour. The absence or presence of breeding colour was a good predictor of testes investment. Compared to males with breeding colour, males without colour were smaller in body size but had extraordinarily large testes. In absolute terms, testes mass of males without breeding colour was on average 3·4 times greater than those of males with breeding colour. Since small colourless males are known to reproduce as sneaker males, this heavy investment in testes probably reflects that they are forced to spawn under sperm competition. Contrary to testes size, sperm‐duct glands were largest among males with breeding colour. These glands produce mucins used for making sperm‐containing mucous trails that males place in the nest before and during spawning. Since both sneakers and nest‐holders potentially could benefit from having large glands, this result is intriguing. Yet, high mucus production may be more important for nest‐holders, because it also protects developing embryos from infections. There was no significant effect of season on body size, testes or sperm‐duct glands size, but colourless males tended to be less common late in the season. Possibly this may indicate that individual small colourless males develop into their more colourful counterparts within the breeding season.     

Agonistic and grooming behavior of captive crowned lemurs (Lemur coronatus) during the breeding season

Captive breeding of rare and endangered prosimians may be enhanced by an increased understanding of all aspects of their seasonal mating behavior. In this study, the agonistic and grooming behaior of captiveL. coronatus were studied during their annual breeding season. Between October and March, selected aspects of agonistic and grooming behavior of four male-female groups were recorded. Males initiated significantly more allogrooming than females. The frequency of this behavior pattern increased significantly in the weeks of estrus. Females performed significantly more agonistic behavior patterns than males. The mean frequency of agonistic interactions decreased significantly during the breeding season. In successfully reproducing groups males showed much less agonism towards females, than they did in unsuccessful groups. Inter-specific comparisons demonstrated that the patterns of agonistic interactions during the breeding season are very different among closely related species of lemurids. The conclusions drawn from this study are that captive breeding of crowned lemurs may be enhanced by keeping permanent multi-male, multi-female groups.     

Latitudinal differences in somatic energy storage: adaptive responses to seasonality in an estuarine fish (Atherinidae: Menidia menidia)

This study focuses on the seasonal accumulation and depletion of somatic energy in the Atlantic silverside (Menidia menidia), an annual estuarine fish. Previous research revealed that northern silversides are subject to strong size-dependent winter mortality, while southern fish suffer no appreciable winter mortality. To examine whether there was geographic differentiation in allocation strategies, we compared temporal patterns of energy storage and utilization among three populations along this gradient in seasonality. The comparative design used monthly or biweekly samples of fish collected in the wild, as well as samples of fish from each population reared in a common environment, where genetic differences can be clarified. Somatic energy stores were quantified via gravimetric analysis of neutral storage lipids and lean tissue. Analysis revealed that small individuals maintained relatively low levels of lipid reserves, which may account for their lower survival in winter. Wild fish in the north rapidly accumulated large somatic reserves, which were depleted over the winter and then increased again during the subsequent spring breeding season. In wild southern fish, relatively small reserves accumulated slowly until breeding commenced in the spring. The common-environment comparison of somatic storage patterns revealed a genetic basis for among-population differences in reserve accumulation rates, but no differences in the amount of reserves stored. We conclude that the overwinter depletion of somatic reserves has a significant selective impact on energy accumulation and allocation strategies in seasonal environments. Received: 1 November 1995 / Accepted: 13 September 1996     

The power of the seasons: rainfall triggers parental care in poison frogs

The quality of breeding sites is of great importance for the reproductive success and accordingly the fitness of many animal species. Hence, individuals should decide carefully where to rear their offspring. Often parents have to account for multiple characteristics of habitat quality at once, which in turn might change over time. Specimens confronted with such variability may evolve the ability to display context-dependant decision plasticity. Anuran amphibians breeding in ephemeral pools largely face two risks for their offspring: desiccation and predation. The Neotropical poison frog Ranitomeya variabilis deposits both eggs and tadpoles in phytotelmata. These small tadpole nurseries lower the risk of offspring predation. However, because most poison frog tadpoles are cannibalistic, even these pools need to be surveyed for predators, and parents tend to avoid deposition with conspecifics. We tested if this avoidance behaviour does change in parental R. variabilis depending on seasonal circumstances. Over several months we provided the frogs the option to deposit their eggs or tadpoles in pools that did and did not contain chemical cues of cannibalistic conspecifics, respectively. During the rainy season, frogs strongly avoided conspecific cues for both eggs and tadpoles. Anyway, with the change to the dry season, parental preferences changed such that parent frogs were more likely to deposit tadpoles (but not eggs) in pools containing cues of conspecific tadpoles. We suggest that R. variabilis, a species that typically isolates its cannibalistic offspring, has evolved a plastic feeding behaviour with regard to the risk of phytotelmata desiccation. We interpret that parents provide older tadpoles with younger ‘trophic’ tadpoles in order to accelerate their development and save them from impending desiccation.     

Spatial and temporal patterns in the fish assemblages of individual pools in a midwestern stream (U.S.A.)

Synopsis The composition and consistency of fish assemblages in 14 adjacent pools (6–120 m long) of a clear-water, limestone and gravel creek in midwestern U.S.A. were quantified in eight snorkeling surveys over 19 months, to establish a baseline of natural variation in the system at this scale. The fauna of the stream was dominated numerically by minnows (Cyprinidae), sunfish and black bass (Centrarchidae), and topminnows (Fundulidae). The pool fish fauna of the total 1 km reach (including all 14 pools) was highly consistent throughout the study, despite two major floods. Assemblages in individual pools generally were consistent, but there was more variation within pools than at the scale of the entire reach. Throughout the study, most individual pools remained within discrete subsets of the total occupied multivariate space in a principal components analysis based on fish species abundances. Sunfishes (Lepomis spp.) and bass (Micropterus spp.) were more consistent in their distribution among pools than were minnows (Cyprinidae) or a topminnow (Fundulus). There were 25 significant correlations in occurrence of species pairs among stream pools, out of 91 possible comparisons of the 14 most abundant taxa in the reach. Many pools contained assemblages either dominated by large centrarchids or by abundant cyprinids and juvenile centrarchids, but intermediate assemblages also were observed. The dynamics of distribution of fish species and fish assemblages among individual stream pools are likely influenced by a combination of species-specific behaviors and habitat selection, predator constraints on use of individual pools by small fishes, riffles as size-selective barriers to fish movements between pools, dispersal of young-of-the-year fishes, and abiotic phenomena like floods. Individual stream pools appear to be discrete habitat units for fishes, and do represent an appropriate scale for biologically meaningful studies of fish assemblages or their effects on streams.Department of Zoology, University of Oklahoma     

Fine-scale genetic structure and its consequence in breeding aggregations of a passerine bird

The pattern of fine-scale genetic structure in a population may reflect current biological processes of the species, such as natal dispersal, the breeding system and demography. We investigated the spatial distribution of nests and fine-scale genetic structure during two breeding seasons in a population of a weakly territorial, flock-living passerine bird, the vinous-throated parrotbill, Paradoxornis webbianus . Nest distribution was clustered. There were two peaks of egg laying within each breeding season, and spatial clustering of nests was more extreme during the second peak after controlling for breeding density. The patterns of genetic structure during the breeding season varied with parental sex and season. Genetic structure occurred during the second laying peak: males breeding within 200 m of one another at this time were significantly more closely related than males breeding farther apart. However, no apparent genetic structure was detected in males during the first laying peak or among females in either laying peak. These results reveal male-oriented kin affiliation during part of the breeding season in this species. Furthermore, juvenile recruitment into the winter flocks was positively related to this increased relatedness among males via kin affiliation. This study implies that fine-scale genetic structure during the breeding season could be a factor determining individual fitness and may play an important role in our understanding of the evolution of social systems.     

Differences in rheotactic responses contribute to divergent habitat use between parapatric lake and stream threespine stickleback

Migration among populations is widely thought to undermine adaptive divergence, assuming gene flow arises from random movement of individuals. If individuals instead differ in dispersal behavior, phenotype‐dependent dispersal can reduce the effective rate of gene flow or even facilitate divergence. For example, parapatric populations of lake and stream stickleback tend to actively avoid dispersing into the adjoining habitat. However, the behavioral basis of this nonrandom dispersal was previously unknown. Here, we show that lake and stream stickleback exhibit divergent rheotactic responses (behavioral response to currents). During the breeding season, wild‐caught inlet stream stickleback were better than lake fish at maintaining position in currents, faced upstream more, and spent more time in low‐current areas. As a result, stream fish expended significantly less energy in currents than did lake fish. These divergent rheotactic responses likely contribute to divergent habitat use by lake and stream stickleback. Although rheotactic differences were absent in nonbreeding fish, divergent behavior of breeding‐season fish may suffice for assortative mating by breeding location. The resulting reproductive isolation between lake and stream fish may explain the fine‐scale evolutionary differentiation in parapatric stickleback populations.     

Dispersal in Kin Coalition Throughout the Non‐Breeding Season to Facilitate Fine‐Scale Genetic Structure in the Breeding Season: Evidence From a Small Passerine

Evidence shows that social cooperation among kin may evolve even in birds with extensive dispersal. In such cases, maintaining kinship during dispersal is essential to the subsequent expression of kin cooperation. This hypothesis has not been examined for most bird species. We addressed it in the ground tit (Parus humilis), a passerine where kin frequently interact in terms of cooperative polygamy and extra‐pair mating despite fast annual turnover of the breeding population. Pedigree and genotype data showed that while groups varied in composition throughout the non‐breeding season due to continual individual emigration and immigration, they always contained kin coalitions consisting of either local or immigrant individuals of different age and sexes. The first‐order kin coalitions, according to the information from local individuals, stemmed from single‐family lineages (siblings and their parents), and the lower‐order ones from neighbouring, related family lineages that merged after fledging. It was probable that immigrants had formed kin coalitions in similar ways before dispersing. Groups broke up in the breeding season. Pairing between unrelated individuals from different coalitions within a group was more likely, whereas related individuals from the same coalition tended to nest near each other. The resulting fine‐scale population genetic structure is expected to facilitate breeding interactions among kin. Our findings give clues to understanding the evolution of social cooperation in relation to dispersal.