Model complexity affects transient population dynamics following a dispersal event: A case study with pea aphids

Stage-structured population models predict transient population dynamics if the population deviates from the stable stage distribution. Ecologists’ interest in transient dynamics is growing because populations regularly deviate from the stable stage distribution, which can lead to transient dynamics that differ significantly from the stable stage dynamics. Because the structure of a population matrix (i.e., the number of life-history stages) can influence the predicted scale of the deviation, we explored the effect of matrix size on predicted transient dynamics and the resulting amplification of population size. First, we experimentally measured the transition rates between the different life-history stages and the adult fecundity and survival of the aphid, Acythosiphon pisum. Second, we used these data to parameterize models with different numbers of stages. Third, we compared model predictions with empirically measured transient population growth following the introduction of a single adult aphid. We find that the models with the largest number of life-history stages predicted the largest transient population growth rates, but in all models there was a considerable discrepancy between predicted and empirically measured transient peaks and a dramatic underestimation of final population sizes. For instance, the mean population size after 20 days was 2394 aphids compared to the highest predicted population size of 531 aphids; the predicted asymptotic growth rate (λmax) was consistent with the experiments. Possible explanations for this discrepancy are discussed. Includes 4 supplemental files.

Population biology of Excirolana armata (Dana, 1853) (Isopoda, Cirolanidae) on an exposed sandy beach in Southeastern Brazil

The reproductive biology and population dynamics of the cirolanid isopod Excirolana armata (Dana, 1853) were analysed through monthly samples from December 2003 to November 2005 on Una beach, Sao Paulo state (24 degrees S), in Southeastern Brazil. Sampling was performed along three transects established from the base of foredunes to the waterline. On Una beach, E. armata showed continuous reproduction with higher abundances of ovigerous females in winter and spring (July-November) with a higher peak of juveniles in spring (November 2004). The fecundity ranged from 2 to 18 eggs/embryos per female, depending on the female length. The incubation period was estimated as 2 months. The life span of males and females was nearly 1 year. The short life span and the high energetic expenditure inherent to reproduction with maternal care, probably kept females from producing more than one brood in their lifetime. When comparing the population of E. armata on Una beach (24 degrees S) with populations in Southern Brazil (32 degrees S), Uruguay (34 degrees S) and Argentina (36 degrees S), it was verified that several biological population traits (length of the smallest juvenile, length of the largest individual, length of the smallest and largest ovigerous females, range of fecundity and life span) tended to increase at higher latitudes, whereas other traits (instantaneous rate of mortality and the curvature parameter of von Bertalanffy growth function) tended to decrease. However, comparing E. armata on Una beach (24 degrees S) with a population situated at a close latitude (25 degrees S), unexpected differences in relation to population structure and to growth demonstrated and reinforced the importance of density-dependent factors over life history traits of E. armata on dissipative beaches.

Evaluating the legacy of landscape history: extinction debt and species credit in bird and small mammal assemblages in the Brazilian Atlantic Forest

There is now an extensive literature on extinction debt following deforestation. However, the potential for species credit in landscapes that have experienced a change from decreasing to expanding forest cover has received little attention. Both delayed responses should depend on current landscape forest cover and on species life-history traits, such as longevity, as short-lived species are likely to respond faster than long-lived species. We evaluated the effects of historical and present-day local forest cover on two vertebrate groups with different longevities understorey birds and non-flying small mammals - in forest patches at three Atlantic Forest landscapes. Our work investigated how the probability of extinction debt and species credit varies (i) amongst landscapes with different proportions of forest cover and distinct trajectories of forest cover change, and (ii) between taxa with different life spans. Our results suggest that the existence of extinction debt and species credit, as well as the potential for their future payment and/or receipt, is not only related to forest cover trajectory but also to the amount of remaining forest cover at the landscape scale. Moreover, differences in bird and small mammal life spans seem to be insufficient to affect differently their probability of showing time-delayed responses to landscape change. Synthesis and applications. Our work highlights the need for considering not only the trajectory of deforestation/regeneration but also the amount of forest cover at landscape scale when investigating time-delayed responses to landscape change. As many landscapes are experiencing a change from decreasing to expanding forest cover, understanding the association of extinction and immigration processes, as well as their interactions with the landscape dynamic, is a key factor to plan conservation and restoration actions in human-altered landscapes.

The 6dF Galaxy Survey: stellar population trends across and through the Fundamental Plane

We present results from an analysis of stellar population parameters for 7132 galaxies in the 6dF Galaxy Survey Fundamental Plane (FP) sample. We bin the galaxies along the axes, v1, v2 and v3, of the tri-variate Gaussian to which we have fitted the galaxy distribution in effective radius, surface brightness and central velocity dispersion (FP space), and compute median values of stellar age, [Fe/H], [Z/H] and [a/Fe]. We determine the directions of the vectors in FP space along which each of the binned stellar population parameters vary most strongly. In contrast to previous work, we find stellar population trends not just with velocity dispersion and FP residual, but with radius and surface brightness as well. The most remarkable finding is that the stellar population parameters vary through the plane (v1 direction) and across the plane (v3 direction), but show no variation at all along the plane (v2 direction). The v2 direction in FP space roughly corresponds to luminosity density. We interpret a galaxys position along this vector as being closely tied to its merger history, such that early-type galaxies with lower luminosity density are more likely to have undergone major mergers. This conclusion is reinforced by an examination of the simulations of Kobayashi, which show clear trends of merger history with v2.

Molecular Surveillance of the Newcastle Disease Virus in Domestic and Wild Birds on the North Eastern Coast and Amazon Biome of Brazil

Brazil is one of the world's largest countries with a rich diversity of wildlife, including resident and migratory wild birds, which may be natural reservoirs of the Newcastle disease virus (NDV). Because Brazil is a major global exporter of chicken meat, the emergence of such a disease may have a huge negative impact not only on the economy due to trade restrictions and embargoes, but also on the quality of life of the population. Samples were collected from 1,022 asymptomatic domestic and wild birds from the Brazilian coast and the Amazon region using tracheal/cloacal swabs and tested by RT-qPCR. The results showed 7 (0.7%) birds were positive for NDV. The positive samples were then isolated in embryonated chicken eggs and their matrix protein genes were partially sequenced, revealing a low-pathogenicity NDV. This study confirms the maintenance of the velogenic-NDV free status of Brazil.

Costs and benefits of temporary brood desertion in a Neotropical harvestman (Arachnida: Opiliones)

Brood desertion is a life history strategy that allows parents to minimize costs related to parental care and increase their future fecundity. The harvestman Neosadocus maximus is an interesting model organism to study costs and benefits of temporary brood desertion because females abandon their clutches periodically and keep adding eggs to their clutches for some weeks. In this study, we tested if temporary brood desertion (a) imposes a cost to caring females by increasing the risk of egg predation and (b) offers a benefit to caring females by increasing fecundity as a result of increased foraging opportunities. With intensive field observations followed by a model selection approach, we showed that the proportion of consumed eggs was very low during the day and it was not influenced by the frequency of brood desertion. The proportion of consumed eggs was higher at night and it was negatively related to the frequency of brood desertion. However, frequent brood desertion did not result in higher fecundity, measured both as the number of eggs added to the current clutch and the probability of laying a second clutch over the course of the reproductive season. Considering that harvestmen are sensitive to dehydration, brood desertion during the day may attenuate the physiological stress of remaining exposed on the vegetation. Moreover, since brood desertion is higher during the day, when egg predation pressure is lower, caring females could be adjusting their maternal effort to the temporal variation in predation risk, which is regarded as the main cost of brood desertion in ectotherms.

How promising is Lasioseius floridensis as a control agent of Polyphagotarsonemus latus?

The blattisociid mite Lasioseius floridensis Berlese was found associated with the broad mite, Polyphagotarsonemus latus (Banks), on gerbera leaves in Mogi das Cruzes, State of Sao Paulo, Brazil. Blattisociid mites are not common on aerial plant parts, except under high air humidity levels. Some Lasioseius species have been mentioned as effective control agents of rice pest mites, but nothing is known about the biology of L. floridensis. The objective of this study was to evaluate whether the observed co-occurrence of L. floridensis and P. latus was just occasional or whether the latter could be important as food source for the former, assumed by laboratory evaluation of the ability of the predator to maintain itself, reproduce and develop on that prey. Biological parameters of L. floridensis were compared when exposed to P. latus and to other items as food. The study showed that mating is a pre-requisite for L. floridensis to oviposit and that oviposition rate was much higher on the soil nematode Rhabditella axei (Cobbold) (Rhabditidae) than on P. latus. Ovipositon on the acarid mite Tyrophagus putrescentiae (Schrank) was about the same as on P. latus, but it was nearly zero when the predator was fed the fungi Aspergillus flavus Link or Penicillium sp., or cattail (Typha sp.) pollen. Survivorship was higher in the presence of pollen and lower in the presence of A. flavus or Penicillium sp. than in the absence of those types of food. Life table parameters indicated that the predator performed much better on R. axei than on P. latus. To evaluate the potential effect of L. floridensis as predator of P. latus, complementary studies are warranted to determine the frequency of migration of L. floridensis to aerial plant parts, when predation on P. latus could occur.

Life-cycle and host preference of Amblyomma ovale (Acari: Ixodidae) under laboratory conditions

This study evaluated for the first time the life cycle of Amblyomma ovale in the laboratory. For this purpose, larvae and nymphs were exposed to Gallus gallus (chickens), Cavia porcellus (guinea pigs), Rattus norvegicus (wistar rats), Oryctolagus cuniculus (domestic rabbits), Calomys callosus (vesper mouse), and Didelphis albiventris (white-eared opossum). Nymphs were also exposed to Nectomys squamipes (South American water rat). Adult ticks were fed on dogs. The life-cycle of A. ovale in laboratory could be completed in an average period of ca. 190 days, considering prefeeding periods of 30 days for each of the parasitic stages. Vesper mice were the most suitable host for A. ovale larvae, whereas water rats were the most suitable host for A. ovale nymphs. Our results, coupled with literature data, strongly indicate that small rodents have an important role in the life history of A. ovale. Chickens (the only avian host used in the present study) showed to be moderately suitable hosts for subadult A. ovale ticks, indicating that wild birds might have a secondary role in the life history of A. ovale. Domestic dogs showed to be highly suitable for the adult stage of A. ovale, in agreement with literature data that indicate that the domestic dog is currently one of the most important hosts of A. ovale adult ticks in Latin America.

Comparison of microsatellites and isozymes in genetic diversity studies of Oryza glumaepatula (Poaceae) populations

The study of the genetic structure of wild plant populations is essential for their management and conservation. Several DNA markers have been used in such studies, as well as isozyme markers. In order to provide a better comprehension of the results obtained and a comparison between markers which will help choose tools for future studies in natural populations of Oryza glumaepatula, a predominantly autogamous species, this study used both isozymes and microsatellites to assess the genetic diversity and genetic structure of 13 populations, pointing to similarities and divergences of each marker, and evaluating the relative importance of the results for studies of population genetics and conservation. A bulk sample for each population was obtained, by sampling two to three seeds of each plant, up to a set of 50 seeds. Amplified products of eight SSR loci were electrophoresed on non-denaturing polyacrylamide gels, and the fragments were visualized using silver staining procedure. Isozyme analyses were conducted in polyacrylamide gels, under a discontinuous system, using six enzymatic loci. SSR loci showed higher mean levels of genetic diversity (A=2.83, p=0.71, A(P)=3.17, H-o=0.081, H-e=0.351) than isozyme loci (A=1.20, p=0.20, A(P)=1.38, H-o=0.006, H-e=0.056). Interpopulation genetic differentiation detected by SSR loci (R-ST=0.631, equivalent to F-ST=0.533) was lower than that obtained with isozymes (F-ST=0.772). However, both markers showed high deviation from Hardy-Weinberg expectations (F-IS=0.744 and 0.899, respectively for SSR and isozymes). The mean apparent outcrossing rate for SSR ((t) over bar (a)=0.14) was higher than that obtained using isozymes ((t) over bar (a)=0.043), although both markers detected lower levels of outcrossing in Amazonia compared to the Pantanal. The migrant number estimation was also higher for SSR (Nm=0.219) than isozymes (Nm=0.074), although a small number for both markers was expected due to the mode of reproduction of this species, defined as mixed with predominance of self fertilization. No correlation was obtained between genetic and geographic distances with SSR, but a positive correlation was found between genetic and geographic distances with isozymes. We conclude that these markers are divergent in detecting genetic diversity parameters in O. glumaepatula and that microsatellites are powerful for detecting information at the intra-population level, while isozymes are more powerful for inter-population diversity, since clustering of populations agreed with the expectations based on the geographic distribution of the populations using this marker. Rev. Biol. Trop. 60 (4): 1463-1478. Epub 2012 December 01.

Molecular surveillance of the Newcastle disease virus in domestic and wild birds on the North Eastern Coast and Amazon biome of Brazil

Brazil is one of the world's largest countries with a rich diversity of wildlife, including resident and migratory wild birds, which may be natural reservoirs of the Newcastle disease virus (NDV). Because Brazil is a major global exporter of chicken meat, the emergence of such a disease may have a huge negative impact not only on the economy due to trade restrictions and embargoes, but also on the quality of life of the population. Samples were collected from 1,022 asymptomatic domestic and wild birds from the Brazilian coast and the Amazon region using tracheal/cloacal swabs and tested by RT-qPCR. The results showed 7 (0.7%) birds were positive for NDV. The positive samples were then isolated in embryonated chicken eggs and their matrix protein genes were partially sequenced, revealing a low-pathogenicity NDV. This study confirms the maintenance of the velogenic-NDV free status of Brazil.

The life histories of the two tropical warblers Sylvia boehmi and Sylvia lugens

Ziel der Arbeit war die Quantifizierung einer Reihe von Lebenszyklusmerkmalen der beiden tropischen Grasmückenarten Sylvia boehmi und S. lugens (Aves: Sylviidae; frühere Gattung Parisoma). 13 Brutpaare beider Arten wurden von 2000 bis 2002 in Kenia beobachtet. Die Daten wurden mit multivariater Statistik und multistate mark-recapture Modellen ausgewertet. Die Lebenszyklusmerkmale der beiden untersuchten Sylvia Arten sind im Vergleich zu den temperaten Sylvia-Arten gekennzeichnet durch kleine Gelege von zwei Eiern, lange Inkubationsperioden (S. boehmi (b.) 15.0 Tage, S. lugens (l.) 14.5 Tage), lange Nestlingsperioden (b. 12.9 Tage, l. 16.0 Tage), und niedrige Nesterfolgsraten (b. 19.4%, l. 33.2%). Der Zeitraum vom Ausfliegen der Jungen bis zu ihrer Unabhängigkeit war mit 58.5 Tagen bei S. boehmi und 37.5 Tagen bei S. lugens vergleichsweise lang und die Überlebensrate der flüggen Jungen in dieser Zeit war relativ hoch (b. 69.2%, l. 55.4%). Die jährliche Überlebensrate der brütenden adulten Tiere betrug bei S. boehmi 71.2% und bei S. lugens 57.2%. Die Saisonalität des Habitats, bedingt durch Regen- und Trockenzeiten, hatte keinen Einfluss auf die monatliche Überlebensrate im Laufe eines Jahres. Trotz hoher Nestprädationsraten gab es keinen klaren Zusammenhang zwischen Prädation und Fütterungsrate, Nestbewachung oder Neststandort.

Die Reproduktion von Dinosauriern, speziell der Sauropoden, und deren Bedeutung für ihren Gigantismus

Es wurde ein Teil der life-history, die Reproduktion, von Dinosauriern, speziell der Sauropoden, den größten bekannten jemals auf der Erde existierenden Landtieren, untersucht, um unter anderem den Zusammenhang zwischen Gigantismus und Reproduktion zu erforschen. Hierzu wurde eine mögliche life-history für Sauropoden, auf Grundlage des heutigen Forschungsstands in der Biologie und der Paläontologie, anhand einer Literaturrecherche erstellt. Des Weiteren wurde ein Modell zur Reproduktion bei ausgestorbenen oviparen Amnioten, basierend auf bestehenden Zusammenhängen zwischen Körpergröße und verschiedenen masse-spezifischen Reproduktionsmerkmalen (Eigewicht, Gelegegewicht, jähr. Gelegegewicht) bei rezenten oviparen Amnioten, erarbeitet. Mit Hilfe dieses Modells und Informationen aus Fossilfunden wurde der Frage nachgegangen, wie diese Reproduktionsmerkmale bei Dinosauriern wahrscheinlich ausgesehen haben. Weiterhin erfolgte die Überprüfung der Hypothese, dass Dinosaurier, insbesondere Sauropoden, eine höhere Reproduktionskapazität hatten als gleich große landlebende Säugetiere, was ersteren im Vergleich zu letzteren ermöglicht haben soll so viel größer zu werden (Janis und Carrano 1992). rnDie Untersuchungen der Zusammenhänge zwischen Körpergewicht und den masse-spezifischen Reproduktionsmerkmalen ergaben, dass das Körpergewicht immer stark mit den untersuchten Reproduktionsmerkmalen korreliert war. Große Vögel und große Reptilien unterscheiden sich in ihrem relativen Eigewicht (Eigewicht/Körpergewicht). Vögel haben relativ größere Eier. Betrachtet man das relative Gelegegewicht oder das relative jährliche Gelegegewicht so wird der Unterschied kleiner bzw. ist zwischen manchen Reptilien- und Vogelgruppen nicht mehr vorhanden. Dinosaurier hatten relative Eigewichte, die zwischen denen von Reptilien und Vögel liegen. Basale Dinosaurier, wie Prosauropoden, waren in ihrer Reproduktion eher reptilien-ähnlich, während vogel-ähnliche Theropoden eine Reproduktion hatten, die sich besser durch ein Vogelmodel beschreiben lässt. Die Reproduktion anderer Dinosaurier, wie Sauropoden und Hadrosaurier, lässt sich nicht eindeutig durch eines der beiden Modelle beschreiben und/oder die Modelle variierten in Abhängigkeit des betrachteten Merkmals. Trotzdem war es möglich für alle untersuchten Dinosaurier eine Abschätzung zur Gelegegröße und der Anzahl der jährlich gelegten Eier zu machen. Diese Schätzungen ergaben, dass die vermutete hohe Reproduktionskapazität von mehreren hundert Eiern pro Jahr nur für extrem große Sauropoden (70 t) haltbar ist. rnMit Ausnahme der Nagetiere fand ich die Unterschiede in der Reproduktionskapazität von Vögeln und Säugetieren, die Janis und Carrano (1992) postulierten, sogar auf der Ebene von Ordnungen. Dinosauriergelege waren größer als die Würfe von gleichgroßen (extrapolierten) Säugetieren während die Gelegegröße von gleichgroßen (extrapolierten) Vögeln ähnlich der von Sauropoden war. Da das Aussterberisiko häufig mit niedriger Reproduktionskapazität korreliert ist, impliziert dies ein geringeres Aussterberisiko großer Dinosaurier im Vergleich zu großen Säugetieren. Populationen sehr großer Dinosaurier, wie der Sauropoden, konnten vermutlich daher, über evolutionäre Zeiträume betrachtet, sehr viel länger existieren als Populationen großer Säugetiere.rn

Age, Sex, and Telomere Dynamics in a Long-Lived Seabird with Male-Biased Parental Care

The examination of telomere dynamics is a recent technique in ecology for assessing physiological state and age-related traits from individuals of unknown age. Telomeres shorten with age in most species and are expected to reflect physiological state, reproductive investment, and chronological age. Loss of telomere length is used as an indicator of biological aging, as this detrimental deterioration is associated with lowered survival. Lifespan dimorphism and more rapid senescence in the larger, shorter-lived sex are predicted in species with sexual size dimorphism, however, little is known about the effects of behavioral dimorphism on senescence and life history traits in species with sexual monomorphism. Here we compare telomere dynamics of thick-billed murres (Uria lomvia), a species with male-biased parental care, in two ways: 1) cross-sectionally in birds of known-age (0-28 years) from one colony and 2) longitudinally in birds from four colonies. Telomere dynamics are compared using three measures: the telomere restriction fragment (TRF), a lower window of TRF (TOE), and qPCR. All showed age-related shortening of telomeres, but the TRF measure also indicated that adult female murres have shorter telomere length than adult males, consistent with sex-specific patterns of ageing. Adult males had longer telomeres than adult females on all colonies examined, but chick telomere length did not differ by sex. Additionally, inter-annual telomere changes may be related to environmental conditions; birds from a potentially low quality colony lost telomeres, while those at more hospitable colonies maintained telomere length. We conclude that sex-specific patterns of telomere loss exist in the sexually monomorphic thick-billed murre but are likely to occur between fledging and recruitment. Longer telomeres in males may be related to their homogamous sex chromosomes (ZZ) or to selection for longer life in the care-giving sex. Environmental conditions appeared to be the primary drivers of annual changes in adult birds.

Immune Activation Reduces Sperm Quality in the Great Tit

Mounting an immune response against pathogens incurs costs to organisms by its effects on important life-history traits, such as reproductive investment and survival. As shown recently, immune activation produces large amounts of reactive species and is suggested to induce oxidative stress. Sperm are highly susceptible to oxidative stress, which can negatively impact sperm function and ultimately male fertilizing efficiency. Here we address the question as to whether mounting an immune response affects sperm quality through the damaging effects of oxidative stress. It has been demonstrated recently in birds that carotenoid-based ornaments can be reliable signals of a male's ability to protect sperm from oxidative damage. In a full-factorial design, we immune-challenged great tit males while simultaneously increasing their vitamin E availability, and assessed the effect on sperm quality and oxidative damage. We conducted this experiment in a natural population and tested the males' response to the experimental treatment in relation to their carotenoid-based breast coloration, a condition-dependent trait. Immune activation induced a steeper decline in sperm swimming velocity, thus highlighting the potential costs of an induced immune response on sperm competitive ability and fertilizing efficiency. We found sperm oxidative damage to be negatively correlated with sperm swimming velocity. However, blood resistance to a free-radical attack (a measure of somatic antioxidant capacity) as well as plasma and sperm levels of oxidative damage (lipid peroxidation) remained unaffected, thus suggesting that the observed effect did not arise through oxidative stress. Towards the end of their breeding cycle, swimming velocity of sperm of more intensely colored males was higher, which has important implications for the evolution of mate choice and multiple mating in females because females may accrue both direct and indirect benefits by mating with males having better quality sperm.

Spatial and temporal variation in population genetic structure of wild Nile tilapia (Oreochromis niloticus) across Africa

Background: Reconstructing the evolutionary history of a species is challenging. It often depends not only on the past biogeographic and climatic events but also the contemporary and ecological factors, such as current connectivity and habitat heterogeneity. In fact, these factors might interact with each other and shape the current species distribution. However, to what extent the current population genetic structure reflects the past and the contemporary factors is largely unknown. Here we investigated spatio-temporal genetic structures of Nile tilapia (Oreochromis niloticus) populations, across their natural distribution in Africa. While its large biogeographic distribution can cause genetic differentiation at the paleo-biogeographic scales, its restricted dispersal capacity might induce a strong genetic structure at micro-geographic scales. Results: Using nine microsatellite loci and 350 samples from ten natural populations, we found the highest genetic differentiation among the three ichthyofaunal provinces and regions (Ethiopian, Nilotic and Sudano-Sahelian) (R(ST) = 0.38 - 0.69). This result suggests the predominant effect of paleo-geographic events at macro-geographic scale. In addition, intermediate divergences were found between rivers and lakes within the regions, presumably reflecting relatively recent interruptions of gene flow between hydrographic basins (R(ST) = 0.24 - 0.32). The lowest differentiations were observed among connected populations within a basin (R(ST) = 0.015 in the Volta basin). Comparison of temporal sample series revealed subtle changes in the gene pools in a few generations (F = 0 - 0.053). The estimated effective population sizes were 23 - 143 and the estimated migration rate was moderate (m similar to 0.094 - 0.097) in the Volta populations. Conclusions: This study revealed clear hierarchical patterns of the population genetic structuring of O. niloticus in Africa. The effects of paleo-geographic and climatic events were predominant at macro-geographic scale, and the significant effect of geographic connectivity was detected at micro-geographic scale. The estimated effective population size, the moderate level of dispersal and the rapid temporal change in genetic composition might reflect a potential effect of life history strategy on population dynamics. This hypothesis deserves further investigation. The dynamic pattern revealed at micro-geographic and temporal scales appears important from a genetic resource management as well as from a biodiversity conservation point of view.