Effects of more frequent and prolonged El Niño events on life-history parameters of the degu, a long-lived and slow-reproducing rodent

Climatic influences on survival and reproductive transitions of big-eared woodrats in California oak woodland

It is known that climatic factors can influence the reproductive performance of small mammal populations. However, this information has not been available for the big-eared woodrat (Neotoma macrotis), a keystone species that inhabits the California central coast ranges south to Mexico and the oak woodlands (Quercus spp.) of the western Sierra Nevada foothills. From 2002 to 2014, we livetrapped woodrats on 1.1-ha study plots in coastal-central California and recorded their age and reproductive status. We analyzed these data by a capture-mark-recapture (CMR) framework to estimate state-specific recapture probability (p) and monthly apparent survival (S) of juvenile, non-reproductive, and reproductive adult female woodrats, and the influence of rain and temperature on S and transition probability (Ψ) of the three states. Rainfall from the previous season did not markedly affect survival rates of the states, with one exception: it decreased the survival of nonreproductive woodrats. Nearly all breeding occurred during the cool, wet winter season. Juvenile woodrats had at least a 0.55 probability of breeding by their first winter, conditional on survival. Temperature during the breeding season had a marked negative influence on transition probability. During winter, survival of nonreproductive adult females was significantly higher than for juvenile and reproductive females, indicating a cost of reproduction. Physiological effects and diminished diet quality due to further climate warming could reduce the reproductive success of female big-eared woodrats with negative consequences on population growth and persistence.

Organs infected with Trypanosoma cruzi and DTU identification in the naturally infected rodent Octodon degus

Chagas disease is a public health problem in America. Its parasite, Trypanosoma cruzi, presents different discrete typing units (DTUs), colonizes organs of mammalian hosts in chronic infections, and presents tropism for particular organs in experimental infections. We evaluated T. cruzi tropism towards organs on the naturally infected rodent Octodon degus, identifying the parasites' DTUs, by means of conventional PCR and hybridization. Almost all the analyzed organs presented T. cruzi. More than 42% of the tested oesophagus, skin, skeletal muscle, brain and intestine showed T. cruzi DNA. Other nine types of organs were infected in over 15%. These results suggest that there is some tropism by T. cruzi in chronically infected O. degus. DTU TcV was present in 92.5% of infected organs with identified DTUs; this DTU is frequently reported in human infections in the Southern Cone of South America. Few organs showed mixed DTU infections. This is one of the few reports on the outcome of chronic natural T. cruzi-infection in wild mammal hosts exposed to naturally infected vectors.

Temporal variation in Trypanosoma cruzi lineages from the native rodent Octodon degus in semiarid Chile

Chagas disease is a zoonosis caused by the protozoan parasite Trypanosoma cruzi and transmitted by triatomine insects to several mammalian species acting as reservoir hosts. In the present study, we assess T. cruzi-prevalence and DTU composition of the endemic rodent Octodon degus from a hyper-endemic area of Chagas disease in Chile. Parasite detection is performed by PCR assays on blood samples of individuals captured in the austral summers of 2010-2013. The infection level in rodents differed in the summers of these four years between 18% and 70%. Overall, infected O. degus showed similar T. cruzi-DTU composition (TcI, TcII, TcV and TcVI lineages) among years, corresponding to single and mixed infection, but the relative importance of each DTU changed among years. In 2013, we detected that only three out of the four T. cruzi-DTU found in O. degus were present in the endemic triatomine Mepria spinolai. We suggest that O. degus, an abundant long-lived rodent, is an important native reservoir of T. cruzi in the wild transmission cycle of Chagas disease and it is able to maintain all the T. cruzi-DTUs described in semiarid Chile.

Marsupial population dynamics in a tropical rainforest: intraspecific competition and nonlinear effect of rainfall

Population fluctuations are the result of the combined action of endogenous (feedback structure) and exogenous factors (large- and local-scale climate variables). In this paper, we used a 13-year time series to identify the feedback structure in a population of the brown 4-eyed opossum Metachirus nudicaudatus and to test a hypothesis on the effects of El Niño Southern Oscillation and rainfall using Royama’s theoretical framework. Metachirus nudicaudatus was regulated by a strong 1st-order negative feedback, with intraspecific competition for food resources as the probable factor governing the endogenous system. Contrary to our expectations, El Niño did not explain the marsupial dynamics better than 1-year lagged rainfall, that may operate in 2 different manners: as a nonlinear perturbation effect influencing the strength of density dependence (intraspecific competition and intraguild predation) or as a lateral perturbation effect influencing the carrying capacity of the environment.

As flutuações populacionais são resultado da ação conjunta de fatores endógenos (estrutura de retroalimentação) e exógenos (variáveis climáticas locais e de larga escala). A partir de uma série temporal de 13 anos, nós identificamos a estrutura de retroalimentação da população da cuíca marrom de quatro olhos Metachirus nudicaudatus , e testamos hipóteses a respeito dos efeitos do El Niño Oscilação Sul e chuva utilizando a abordagem teórica de Royama. Metachirus nudicaudatus é regulado por uma forte retroalimentação negativa de primeira ordem, com a competição intraespecífica por recursos alimentares como o provável fator que rege o sistema endógeno. Ao contrário do que esperávamos, o El Niño não explicou a dinâmica populacional deste marsupial melhor do que a chuva com a defasagem de 1 ano, que pode atuar em duas formas: como um efeito de perturbação não-linear, influenciando a força da dependência densidade (competição intraespecífica e predação intraguilda), ou como um efeito de perturbação lateral, influenciando a capacidade de suporte do ambiente.

Spatial distribution of an infectious disease in a small mammal community

Chagas disease is a zoonosis caused by the parasite Trypanosoma cruzi and transmitted by insect vectors to several mammals, but little is known about its spatial epidemiology. We assessed the spatial distribution of T. cruzi infection in vectors and small mammals to test if mammal infection status is related to the proximity to vector colonies. During four consecutive years we captured and georeferenced the locations of mammal species and colonies of Mepraia spinolai, a restricted-movement vector. Infection status on mammals and vectors was evaluated by molecular techniques. To examine the effect of vector colonies on mammal infection status, we constructed an infection distance index using the distance between the location of each captured mammal to each vector colony and the average T. cruzi prevalence of each vector colony, weighted by the number of colonies assessed. We collected and evaluated T. cruzi infection in 944 mammals and 1976 M. spinolai. We found a significant effect of the infection distance index in explaining their infection status, when considering all mammal species together. By examining the most abundant species separately, we found this effect only for the diurnal and gregarious rodent Octodon degus. Spatially explicit models involving the prevalence and location of infected vectors and hosts had not been reported previously for a wild disease.

Infection with Trypanosoma cruzi TcII and TcI in free-ranging population of lion tamarins (Leontopithecus spp): an 11-year follow-up

Here, we present a review of the dataset resulting from the 11-years follow-up of Trypanosoma cruzi infection in free-ranging populations of Leontopithecus rosalia (golden lion tamarin) and Leontopithecus chrysomelas (golden-headed lion tamarin) from distinct forest fragments in Atlantic Coastal Rainforest. Additionally, we present new data regarding T. cruzi infection of small mammals (rodents and marsupials) that live in the same areas as golden lion tamarins and characterisation at discrete typing unit (DTU) level of 77 of these isolates. DTU TcII was found to exclusively infect primates, while TcI infected Didelphis aurita and lion tamarins. The majority of T. cruzi isolates derived from L. rosalia were shown to be TcII (33 out 42) Nine T. cruzi isolates displayed a TcI profile. Golden-headed lion tamarins demonstrated to be excellent reservoirs of TcII, as 24 of 26 T. cruzi isolates exhibited the TcII profile. We concluded the following: (i) the transmission cycle of T. cruzi in a same host species and forest fragment is modified over time, (ii) the infectivity competence of the golden lion tamarin population fluctuates in waves that peak every other year and (iii) both golden and golden-headed lion tamarins are able to maintain long-lasting infections by TcII and TcI.

Effects of mammal host diversity and density on the infection level of Trypanosoma cruzi in sylvatic kissing bugs

Several reports have described host species diversity and identity as the most important factors influencing disease risk, producing either dilution or amplification of the pathogen in a host community. Triatomine vectors, mammals and the protozoan Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) Chagas are involved in the wild cycle of Chagas disease, in which infection of mammals occurs by contamination of mucous membranes or skin abrasions with insect-infected faeces. We examined the extent to which host diversity and identity determine the infection level observed in vector populations (i.e. disease risk in humans). We recorded infection in triatomine colonies and on the coexisting host mammalian species in semi-arid Chile. Host diversity, and total and infected host species densities are used as predictor variables for disease risk. Disease risk did not correlate with host diversity changes. However, the densities of each infected rodent species were positively associated with disease risk. We suggest that the infected host density surrounding the vector colonies is a relevant variable for disease risk and should be considered to understand disease dynamics. It is crucial to pay attention on the spatial scale of analysis, considering the pattern of vector dispersal, when the relationship between host diversity and disease risk is studied.

Fecal cortisol levels predict breeding but not survival of females in the short-lived rodent, Octodon degus

The cort-adaptation hypothesis indicates that an association between glucocorticoid (cort) levels and fitness may vary with the extent to which reproduction or breeding effort is a major determinant of cort levels. Support for a context dependent association between cort and fitness comes mostly from relatively long-lived, bird species. We tested the hypothesis that there are gender and context (life-history) specific cort-fitness relationships in degus, a short-lived and generally semelparous social rodent. In particular, we used demographical records on a natural population to estimate adult survival through seasons and years and linked that to records of baseline cort (based on fecal cortisol metabolites). We found no evidence for a direct relationship between baseline cort and adult survival across seasons, and this lack of association was recorded irrespective of sex and life history stage. Yet, cort levels during early lactation predicted the probability that females produce a second litter during the same breeding season, supporting a connection between baseline cort levels and breeding effort. Overall, the differential effects of cort on survival and breeding supported that the extent of cort-fitness relationships depends on the fitness component examined.

Persistent carry-over effects of planktonic exposure to ocean acidification in the Olympia oyster

Predicting impacts of global environmental change is challenging due to the complex life cycles that characterize many terrestrial and aquatic taxa. Different life stages often interact with the physical environment in distinct ways, and a growing body of work suggests that stresses experienced during one life stage can "carry over" to influence subsequent stages. Assessments of population responses to environmental perturbation must therefore consider how effects might propagate across life-history transitions. We investigated consequences of ocean acidification (decreased pH and carbonate saturation) for early life stages of the Olympia oyster (Ostrea lurida), a foundation species in estuaries along the Pacific coast of North America. We reared oysters at three levels of seawater pH, including a control (8.0) and two additional levels (7.9 and 7.8). Oysters were cultured through their planktonic larval period to metamorphosis and into early juvenile life. Larvae reared under pH 7.8 exhibited a 15% decrease in larval shell growth rate, and a 7% decrease in shell area at settlement, compared to larvae reared under control conditions. Impacts were even more pronounced a week after settlement, with juveniles that had been reared as larvae under reduced pH exhibiting a 41% decrease in shell growth rate. Importantly, the latter effect arose regardless of the pH level the oysters experienced as juveniles, indicating a strong carry-over effect from the larval phase. Adverse impacts of early exposure to low pH persisted for at least 1.5 months after juveniles were transferred to a common environment. Overall, our results suggest that a stringent focus on a single phase of the life cycle (e.g., one perceived as the "weakest link") may neglect critical impacts that can be transferred across life stages in taxa with complex life histories.

Field assessment of Trypanosoma cruzi infection and host survival in the native rodent Octodon degus

Chagas disease is a zoonosis caused by the flagellated parasite Trypanosoma cruzi and transmitted by triatomine insects to several mammalian species acting as reservoir hosts. In the present study, we assess T. cruzi-prevalence, survivorship and T. cruzi-infection rate of the endemic rodent Octodon degus from a hyper-endemic area of Chagas disease in Chile. Parasite detection is performed by PCR assays on blood samples of individuals captured in austral summer of 2010, and on non-infected individuals recaptured in 2011 as well as on new captures. Results show a high infection level in this species (up to 70%). Infected O. degus have the same chance of surviving to the next reproductive season as uninfected individuals, irrespective of sex. We suggest that O. degus, an abundant long-lived rodent with high dispersal capability, could be considered an important native reservoir of T. cruzi in the wild transmission cycle of Chagas disease in Chile.

Extreme climatic events change the dynamics and invasibility of semi-arid annual plant communities

Extreme climatic events represent disturbances that change the availability of resources. We studied their effects on annual plant assemblages in a semi-arid ecosystem in north-central Chile. We analysed 130 years of precipitation data using generalised extreme-value distribution to determine extreme events, and multivariate techniques to analyse 20 years of plant cover data of 34 native and 11 exotic species. Extreme drought resets the dynamics of the system and renders it susceptible to invasion. On the other hand, by favouring native annuals, moderately wet events change species composition and allow the community to be resilient to extreme drought. The probability of extreme drought has doubled over the last 50 years. Therefore, investigations on the interaction of climate change and biological invasions are relevant to determine the potential for future effects on the dynamics of semi-arid annual plant communities.

Characterization of the estrous cycle in Octodon degus

We characterized the reproductive cycle of Octodon degus to determine whether reproductive maturation is spontaneous in juveniles and if ovarian cyclicity and luteal function are spontaneous in adults. Laboratory-reared prepubertal and adult females were monitored for vaginal patency and increased wheel-running. Sexual receptivity was assessed by pairing adult females with a male 1) continuously, 2) at the time of vaginal patency, or 3) following estradiol treatment. Blood samples were assayed for estradiol and progesterone concentrations on Days 1, 4, 8, and 16 relative to vaginal opening. Ovarian tissues were collected 6 and 16 days after behavioral estrus and 6 days after copulation for histology. In juveniles, the onset of cyclic vaginal patency and increased wheel-running activity was spontaneous, occurred in the absence of proximal male cues, and appeared at regular intervals (17.5 ± 1.4 days). In adults, vaginal patency and increased wheel-running occurred cyclically (21.2 ± 0.6 days) in the absence of proximal male cues, and these traits predicted the time of sexual receptivity. Corpora lutea develop spontaneously and are maintained for 12-14 days. The ovaries had well-developed corpora lutea 6 days after mating and 6 days after estrus without mating. Progesterone concentrations were highest in the second half of the cycle when corpora lutea were present and estradiol concentrations peaked on the day of estrus. Thus, female degus appear to exhibit a spontaneous reproductive cycle consistent with other Hystricognathi rodents. Octodon degus is a novel model with which to examine the mechanisms underlying different reproductive cycles.