First fossil gravid turtle provides insight into the evolution of reproductive traits in turtles

Here we report on the first discovery of shelled eggs inside the body cavity of a fossil turtle and on an isolated egg clutch, both referable to the Cretaceous turtle Adocus. These discoveries provide a unique opportunity to gain insight into the reproductive traits of an extinct turtle and to understand the evolution of such traits among living turtles. The gravid adult and egg clutch indicate that Adocus laid large clutches of rigid-shelled spherical eggs and established their nests near rivers, traits that are shared by its closest living relatives, the soft-shelled turtles. Adocus eggshell, however, was probably more rigid than that of living turtles, based on its great thickness and structure, features that may represent unique adaptations to intense predation or to arid nest environments. In light of the reproductive traits observed in Adocus, the distribution of reproductive traits among turtles reveals that large clutches of rigid-shelled eggs are primitive for hidden-necked turtles (cryptodirans) and that spherical eggs may have evolved independently within this group.     

The trade-off between dispersability and longevity - an important aspect of plant species diversity

Abstract. Local presence of plant species is determined by population colonizations and extinctions. All traits that influence the capacity of individuals to colonize patches and survive within patches, are therefore important for community diversity. Spatial models can explain the coexistence of species provided that the inferior competitor has a greater spatial mobility and thereby can avoid competition. We searched the literature for empirical evidence for such trade-offs and included all available information on correlations between traits associated with the capacity to colonize and traits promoting the ability to survive. A lower reproductive effort of a species is associated with a longer life span and a higher competitive ability. Morphological adaptations for dispersal are less common in species which better tolerate stress, that are better competitors or possess seed dormancy. Such patterns suggest that species that are good survivors may have a limited ability to colonize new patches and vice versa. A negative correlation between dispersability and longevity has important effects on the regional dynamics of single species as well as on the coexistence of species. From a conservation perspective differences in the colonization capacity among species imply that restoration of plant biodiversity must not only focus on conditions within patches, but also consider the spatial arrangement of patches in order to enable plants to bridge gaps in time and space.     

Restricted dispersal reduces the strength of spatial density dependence in a tropical bird population

Spatial processes could play an important role in density-dependent population regulation because the disproportionate use of poor quality habitats as population size increases is widespread in animal populations-the so-called buffer effect. While the buffer effect patterns and their demographic consequences have been described in a number of wild populations, much less is known about how dispersal affects distribution patterns and ultimately density dependence. Here, we investigated the role of dispersal in spatial density dependence using an extraordinarily detailed dataset from a reintroduced Mauritius kestrel (Falco punctatus) population with a territorial (despotic) breeding system. We show that recruitment rates varied significantly between territories, and that territory occupancy was related to its recruitment rate, both of which are consistent with the buffer effect theory. However, we also show that restricted dispersal affects the patterns of territory occupancy with the territories close to release sites being occupied sooner and for longer as the population has grown than the territories further away. As a result of these dispersal patterns, the strength of spatial density dependence is significantly reduced. We conclude that restricted dispersal can modify spatial density dependence in the wild, which has implications for the way population dynamics are likely to be impacted by environmental change.     

Population dynamics and sex ratio of a parasitoid altered by fungal-infected diet of host butterfly

Variation of host quality affects population dynamics of parasitoids, even at the landscape scale. What causes host quality to vary and the subsequent mechanisms by which parasitoid population dynamics are affected can be complex. Here, we examine the indirect interaction of a plant pathogen with a parasitoid wasp. Under laboratory conditions, parasitoids from hosts fed fungus-infected plants weighed less than those from hosts fed uninfected plants, indicating that the fungus causes the hosts to be of poor quality. However, parasitoids reared from hosts fed fungal-infected diet also tended to be female, a characteristic associated with high host quality. The pathogen, herbivore and parasitoid persist regionally as metapopulations in a shared landscape in Aland, Finland. In an analysis of the metapopulation dynamics of the parasitoid over 6 years, the probability of colonization of a host population increased by more than twofold in patches occupied by the plant pathogen. While we cannot determine that the relationship is causal, a compelling explanation is that the plant pathogen facilitates the establishment by the parasitoid by increasing the fraction of female offspring. This is a novel mechanism of spatial multi-trophic level interactions.     

Spatial niche partitioning in dinosaurs from the latest cretaceous (Maastrichtian) of North America

We examine patterns of occurrence of associated dinosaur specimens (n = 343) from the North American Upper Cretaceous Hell Creek Formation and equivalent beds, by comparing their relative abundance in sandstone and mudstone. Ceratopsians preferentially occur in mudstone, whereas hadrosaurs and the small ornithopod Thescelosaurus show a strong association with sandstone. By contrast, the giant carnivore Tyrannosaurus rex shows no preferred association with either lithology. These lithologies are used as an indicator of environment of deposition, with sandstone generally representing river environments, and finer grained sediments typically representing floodplain environments. Given these patterns of occurrence, we argue that spatial niche partitioning helped reduce competition for resources between the herbivorous dinosaurs. Within coastal lowlands ceratopsians preferred habitats farther away from rivers, whereas hadrosaurs and Thescelosaurus preferred habitats in close proximity to rivers, and T. rex, the ecosystem's sole large carnivore, inhabited both palaeoenvironments. Spatial partitioning of the environment helps explain how several species of large herbivorous dinosaurs coexisted. This study emphasizes that different lithologies can preserve dramatically dissimilar vertebrate assemblages, even when deposited in close proximity and within a narrow window of time. The lithology in which fossils are preserved should be recorded as these data can provide unique insights into the palaeoecology of the animals they preserve.     

Population dynamics of epiphytic orchids in a metapopulation context

Background and Aims

Populations of many epiphytes show a patchy distribution where clusters of plants growing on individual trees are spatially separated and may thus function as metapopulations. Seed dispersal is necessary to (re)colonize unoccupied habitats, and to transfer seeds from high- to low-competition patches. Increasing dispersal distances, however, reduces local fecundity and the probability that seeds will find a safe site outside the original patch. Thus, there is a conflict between seed survival and colonization.

Methods

Populations of three epiphytic orchids were monitored over three years in a Mexican humid montane forest and analysed with spatially averaged and with spatially explicit matrix metapopulation models. In the latter, population dynamics at the scale of the subpopulations (epiphytes on individual host trees) are based on detailed stage-structured observations of transition probabilities and trees are connected by a dispersal function.

Key Results

Population growth rates differed among trees and years. While ignoring these differences, and averaging the population matrices over trees, yields negative population growth, metapopulation models predict stable or growing populations because the trees that support growing subpopulations determine the growth of the metapopulation. Stochastic models which account for the differences among years differed only marginally from deterministic models. Population growth rates were significantly lower, and extinctions of local patches more frequent in models where higher dispersal results in reduced local fecundity compared with hypothetical models where this is not the case. The difference between the two models increased with increasing mean dispersal distance. Though recolonization events increased with dispersal distance, this could not compensate the losses due to reduced local fecundity.

Conclusions

For epiphytes, metapopulation models are useful to capture processes beyond the level of the single host tree, but local processes are equally important to understand epiphyte population dynamics.     

Effects of local extinction of the plains vizcacha (Lagostomus maximus) on vegetation patterns in semi-arid scrub

We studied spatial and temporal effects of local extinction of the plains vizcacha (Lagostomus maximus) on plant communities following widespread, natural extinctions of vizcachas in semi-arid scrub of Argentina. Spatial patterns in vegetation were examined along transects extending outward from active and extinct vizcacha burrow systems. Responses of vegetation to removal of vizcachas were assessed experimentally with exclosures and by documenting vegetation dynamics for 6 years following extinctions. Transect data demonstrated clear spatial patterns in plant cover, particularly an increase in perennial grasses, outward from active vizcacha burrows. These patterns were consistent with predictions based on foraging theory and studies that document grasses as the preferred food of vizcachas. Removal of vizcachas, experimentally and with extinctions, resulted in an immediate increase in perennial and annual forbs indicating that intense herbivory can depress forb cover, as well as grasses. After a 1-year lag following cessation of herbivory, cover of grasses increased. Forbs declined as grasses increased. The long-term effect of extinction of vizcachas was a conversion of colony sites from open patches dominated by forbs to dense bunch grass characteristic of the matrix. Major changes in vegetation occurred within 2–3 years after extinction, resulting in a large pulse of landscape change. However, some species of grasses were uncommon until 5–6 years after the vizcacha extinction. With extinction and colonization, vizcachas generate a dynamic mosaic of patches on the landscape and create temporal, as well as spatial, heterogeneity in semi-arid scrub.     

Incubation capacity limits maximum clutch size in black-tailed gulls Larus crassirostris

Factors determining clutch size of birds have long been the central issue in studies in life histories. It is assumed that the configuration of brood patches could limit the maximum clutch size. To test this hypothesis we manipulated clutch sizes and measured egg temperature as well as reproductive consequences in black-tailed gulls Larus crassirostris , which usually lay two egg clutches and have three brood patches. Mean egg temperature in 4-egg clutches (32.6±1.0°C) was significantly lower than in 2-egg (34.6±0.4°C) and 3-egg clutches (34.1±0.4°C), because egg temperature of the coolest egg within a 4-egg clutch was often substantially lower than the other three eggs. The proportion of eggs hatching from 4-egg clutches (11.6%) was lower than those of 2-egg (49.1%) and 3-egg clutches (52.0%). Four-egg clutches had longer incubation periods (29.6±1.3 day) than 2-egg (28.1±1.7 day) and 3-egg clutches (28.0 ±1.3 day). The results indicate that incubation capacity, which may be determined by the configuration of brood patches, limits the maximum clutch size in black tailed gulls, but not the actual clutch size typically laid.     

Variation in reproductive output of marine turtles

Most marine turtle species are non-annual breeders and show variation in both the number of eggs laid per clutch and the number of clutches laid in a season. Large levels of inter-annual variation in the number of nesting females have been well documented in green turtle nesting populations and may be linked to environmental conditions. Other species of marine turtle exhibit less variation in nesting numbers. This inter-specific difference is thought to be linked to trophic status. To examine whether individual reproductive output is more variable in the herbivorous green turtle (Chelonia mydas Linneaeus 1758) than the carnivorous loggerhead (Caretta caretta Linneaeus 1758), we examined the nesting of both species in Cyprus over nine seasons. Green turtles showed slower annual growth rates (0.11 cm year⁻¹ curved carapace length (CCL) and 0.27 cm year⁻¹ curved carapace width (CCW)) than loggerhead turtles (0.36 cm year⁻¹ CCL, 0.51 cm year⁻¹ CCW). CCL was highly correlated to mean clutch size in both green (R²=0.51) and loggerhead turtles (R²=0.61) and maximal clutch size of green turtles (R²=0.58). Larger females did not lay a greater number of clutches or have a shorter remigration interval than smaller females of either species. On average, the size of green turtle clutches increased and that of loggerhead turtles decreased as the season progressed. Individual green turtles, however, produced more eggs per clutch through the season to a maximum in the third or fourth clutch. In loggerhead turtles, clutches 1-4 were very similar in size but the fifth clutch was 38% smaller than the first. No individuals of either species were recorded laying more than five clutches. Green turtles may not be able to achieve their maximum reproductive output with respect to clutch size throughout the season, whereas only loggerhead turtles laying five clutches (n=5) appear to become resource depleted. Green turtles nesting in years when large numbers of nests were recorded laid a greater number of clutches than females nesting in years with lower levels of nesting.     

Habitat quality as a predictor of spatial variation in blue tit reproductive performance: a multi-plot analysis in a heterogeneous landscape

Vertebrate studies have rarely investigated the influence of spatial variation in habitat richness on both short-term (breeding) and long-term (offspring recruitment) reproductive performance using simultaneously multi-patch, multi-habitat type and multi-year approaches at landscape level. Here we present results of such an approach using the influence of two oak tree (Quercus ilex, Q. humilis) species on reproductive performance in Corsican blue tits (Parus caeruleus ogliastrae) as a model system. We found that blue tits breeding in rich broad-leaved deciduous patches consistently laid eggs earlier in the season, and produced larger clutches and more fledglings of higher quality, than those breeding in poor evergreen patches. Also, parents, especially males, were in better physical condition in the broad-leaved deciduous than in the evergreen patches. Surprisingly, estimates of long-term effects of reproduction, such as recruitment rates of locally born offspring, did not differ between the two habitat types. Our results suggest that short-term breeding performance and phenotypic quality of both chicks and parents do not necessarily provide reliable information about contributions to following generations at a scale larger than that of the local study plot. Differences in reproductive performance between the two oak habitat types could not be attributed to density-dependent effects, differences in levels of nest predation, or differences in age structure of the birds. We suggest that habitats that are optimal for breeding are not necessarily optimal for survival after the breeding season.     

Size-selective dispersal of Daphnia resting eggs by backswimmers (Notonecta maculata)

Freshwater zooplankton is increasingly used to study effects of dispersal on community and metacommunity structure. Yet, it remains unclear how zooplankton disperses. Clearly, birds and wind play a significant role as zooplankton dispersal agents, but they may not always be the main vectors. This experimental study shows that a cosmopolitan aquatic insect, Notonecta, can be an important vector of cladoceran resting eggs (ephippia). Dispersing Notonecta frequently transported ephippia during flight, with a bias towards smaller ephippia in two species. A similar trend was present at the species level: Daphnia species with smaller ephippia were more often dispersed, suggesting that Notonecta could generate specific colonist communities. In addition, buoyancy appeared a critical trait, as non-floating ephippia of Daphnia magna were never dispersed. Our data suggest that Notonecta could be important dispersers of Daphnia, and that knowledge of dispersal dynamics of Notonecta may be used to predict Daphnia dispersal, colonization and resilience to disturbance.     

Effects of live coral,epilithic algal communities and substrate type on algal recruitment

The recruitment of algae is a critical process during algal colonization and invasions, including coral-to-algal phase shifts. Although algae are widely assumed to colonize and kill corals, there is very little known about the recruitment dynamics of coral reef algae. This study tested the ability of two dominant macroalgae (Fucales including Sargassum spp. and Lobophora variegata) to settle and grow on healthy coral tissue. The study also explored the effects of interactions with prior occupants, and of abiotic substrate properties (texture, and ceramic and carbonate material). The results indicate that healthy corals were able to prevent attachment or survival of recruits of these macroalgae. This is a significant point, since it suggests that the replacement of corals by algae may often require prior stress or death in the coral tissue. Pre-conditioning of plates at different sites had some effects, but these were relatively minor, whereas there was considerable variation within sites. Some of this variation appeared to be related to the amount of turf algae or crustose coralline algae on the plates. Recruitment was generally, but not always, higher on plates with rougher texture. Overall, this preliminary exploration indicates considerable potential for variability in outcomes of algal colonization, with implications for the dynamics of algal invasions. In particular, the results do not support suggestions that planktonic algal propagules can directly settle on and colonize healthy coral tissue.Communicated by Topic Editor D. Barnes     

Male attractiveness regulates daughter fecundity non-genetically via maternal investment

Mothers can non-genetically influence offspring phenotype in response to environmental conditions, including mate attractiveness. If such 'maternal effects' influence the offspring's reproduction and F2 generation, there is a mechanism for non-genetic trans-generational effects on phenotype, including epigenetic phenomena, with implications for evolution and population dynamics. We demonstrate in the zebra finch Taeniopygia guttata such non-genetic effects on offspring fecundity and the size of early stage F2 (eggs) in response to experimentally manipulated father's attractiveness. Our experimental design allowed us to deduce that the mechanism for this non-genetic paternal effect was via maternal investment in eggs. This affected female offspring size and, consequently, fecundity and F2 (egg) size. This demonstrates that female perception of mate attractiveness can have non-genetic, trans-generational fitness consequences and this may have important implications for the evolution of sexually selected traits and population dynamics.     

A parasitoid wasp uses landmarks while monitoring potential resources

Social insects and insects that provision nests are well known to have complex foraging behaviour involving repeated visits to learned locations. Other insects do not forage from a central location and are generally assumed to respond to resources by simple attraction without spatial memory. This simple response to resource cues is generally taken as giving rise to patterns of resource use that correspond directly to resource distribution. By contrast, the solitary parasitoid wasp Hyposoter horticola monitors the locations of multiple potential hosts (butterfly eggs) for up to several weeks, until the hosts become susceptible to parasitism. Essentially all hosts in the landscape are found, and one-third of them are parasitized, independent of host density. Here, we show that the wasps do not relocate hosts using odour markers previously left by themselves or other foragers, nor do they find the eggs anew repeatedly. Instead, the wasps relocate host eggs by learning the position of the eggs relative to visual landmarks. The anticipatory foraging behaviour presented here is a key to the wasp's exceptionally stable population dynamics.     

Proteus mirabilis interkingdom swarming signals attract blow flies

Flies transport specific bacteria with their larvae that provide a wider range of nutrients for those bacteria. Our hypothesis was that this symbiotic interaction may depend on interkingdom signaling. We obtained Proteus mirabilis from the salivary glands of the blow fly Lucilia sericata; this strain swarmed significantly and produced a strong odor that attracts blow flies. To identify the putative interkingdom signals for the bacterium and flies, we reasoned that as swarming is used by this bacterium to cover the food resource and requires bacterial signaling, the same bacterial signals used for swarming may be used to communicate with blow flies. Using transposon mutagenesis, we identified six novel genes for swarming (ureR, fis, hybG, zapB, fadE and PROSTU_03490), then, confirming our hypothesis, we discovered that fly attractants, lactic acid, phenol, NaOH, KOH and ammonia, restore swarming for cells with the swarming mutations. Hence, compounds produced by the bacterium that attract flies also are utilized for swarming. In addition, bacteria with the swarming mutation rfaL attracted fewer blow flies and reduced the number of eggs laid by the flies. Therefore, we have identified several interkingdom signals between P. mirabilis and blow flies.     

Sickness behaviour acting as an evolutionary trap? Male house finches preferentially feed near diseased conspecifics

Host behaviour towards infectious conspecifics is a crucial yet overlooked component of pathogen dynamics. Selection is expected to favour individuals who can recognize and avoid infected conspecifics in order to reduce their own risk of infection. However, evidence is scarce and limited to species employing chemical cues. Here, we experimentally examine whether healthy captive house finches (Carpodacus mexicanus) preferentially forage near a same-sex, healthy conspecific versus one infected with the directly transmissible pathogen Mycoplasma gallisepticum (MG), which causes lethargy and visible conjunctivitis. Interestingly, male house finches strongly preferred feeding near diseased conspecifics, while females showed no preference. This sex difference appeared to be the result of lower aggression rates in diseased males, but not in females. The reduced aggression of diseased males may act as an ‘evolutionary trap’ by presenting a historically beneficial behavioural cue in the context of a new environment, which now includes a recently emerged, potentially fatal pathogen. Since MG can be directly transmitted during feeding, healthy males may inadvertently increase their risk of contracting MG. This behaviour is likely to significantly contribute to the continued persistence of MG epidemics in wild populations.     

Stoats (Mustela erminea) provide evidence of natural overland colonization of Ireland

The current Irish biota has controversial origins. Ireland was largely covered by ice at the Last Glacial Maximum (LGM) and may not have had land connections to continental Europe and Britain thereafter. Given the potential difficulty for terrestrial species to colonize Ireland except by human introduction, we investigated the stoat (Mustela erminea) as a possible cold-tolerant model species for natural colonization of Ireland at the LGM itself. The stoat currently lives in Ireland and Britain and across much of the Holarctic region including the high Arctic. We studied mitochondrial DNA variation (1771 bp) over the whole geographical range of the stoat (186 individuals and 142 localities), but with particular emphasis on the British Isles and continental Europe. Irish stoats showed considerably greater nucleotide and haplotype diversity than those in Britain. Bayesian dating is consistent with an LGM colonization of Ireland and suggests that Britain was colonized later. This later colonization probably reflects a replacement event, which can explain why Irish and British stoats belong to different mitochondrial lineages as well as different morphologically defined subspecies. The molecular data strongly indicate that stoats colonized Ireland naturally and that their genetic variability reflects accumulation of mutations during a population expansion on the island.     

Herbivore response to vegetational diversity: spatial interaction of resources and natural enemies

Vegetational diversity in agricultural systems is predicted to reduce herbivore populations, but we observed the opposite effect: higher nymph population densities of a functionally monophagous herbivore, the squash bug, Anasa tristis (Hemiptera: Coreidae) in a vegetationally diverse squash-bean-corn polyculture than in a squash monoculture. We examined spatial and temporal aspects of squash bug and predator populations in relation to vegetational diversity. Average colonization, oviposition, and mortality rates for the herbivore were similar in monocultures and polycultures. In the polyculture, however, we found that squash bugs eggs were highly aggregated on plants on the outer edges of plots. Predation was also lower on plants near the edges, allowing the large aggregations of eggs found in the polyculture to escape predation and ultimately produce more squash bugs. Spatial interactions between herbivores and natural enemies may underlie some of the general effects of vegetational diversity on herbivores.     

Spatial and temporal genetic structure in a hybrid cordgrass invasion

Invasive hybrids and their spread dynamics pose unique opportunities to study evolutionary processes. Invasive hybrids of native Spartina foliosa and introduced S. alterniflora have expanded throughout San Francisco Bay intertidal habitats within the past 35 years by deliberate plantation and seeds floating on the tide. Our goals were to assess spatial and temporal scales of genetic structure in Spartina hybrid populations within the context of colonization history. We genotyped adult and seedling Spartina using 17 microsatellite loci and mapped their locations in three populations. All sampled seedlings were hybrids. Bayesian ordination analysis distinguished hybrid populations from parent species, clearly separated the population that originated by plantation from populations that originated naturally by seed and aligned most seedlings within each population. Population genetic structure estimated by analysis of molecular variance was substantial (F_ST=0.21). Temporal genetic structure among age classes varied highly between populations. At one population, the divergence between adults and 2004 seedlings was low (F_ST=0.02) whereas at another population this divergence was high (F_ST=0.26). This latter result was consistent with local recruitment of self-fertilized seed produced by only a few parental plants. We found fine-scale spatial genetic structure at distances less than ∼200 m, further supporting local seed and/or pollen dispersal. We posit a few self-fertile plants dominating local recruitment created substantial spatial genetic structure despite initial long-distance, human dispersal of hybrid Spartina through San Francisco Bay. Fine-scale genetic structure may more strongly develop when local recruits are dominated by the offspring of a few self-fertile plants.     

Fergusobia/Fergusonina-induced Shoot Bud Gall Development on Melaleuca quinquenervia

Fergusobia nematodes and Fergusonina flies are mutualists that cause a variety of gall types on myrtaceous plant buds and young leaves. The biology of an isolate of the gall complex was studied in its native range in Australia for possible use in southern Florida as a biological control agent against the invasive broad-leaved paperbark tree, Melaleuca quinquenervia. Timed studies with caged Fergusonina flies on young branches of M. quinquenervia revealed that females are synovigenic with lifetime fecundities of 183 ± 42 (standard error; SE) eggs and longevities of 17 ± 2 days. None of the male flies but all dissected female flies contained parasitic female nematodes (range = 3-15), nematode eggs (12-112), and nematode juveniles (78-1,750). Female flies deposited eggs (34 ± 6; 8-77 per bud) and nematode juveniles (114 ± 15; 44-207 per bud) into bud apices within 15 days. Histological sections of shoot buds suggested that nematodes induce the formation of hypertrophied, uninucleate plant cells prior to fly larval eclosion. Enlarged size, granular cytoplasm, and enlarged nucleus and nucleolus characterized these cells, which appeared similar to those of other species galled by nematodes in the Anguinidae. Observations of ovipositional behavior revealed that female Fergusonina sp. create diagnostic oviposition scars. The presence of these scars may facilitate recognition of host use during specificity screening.