Counterintuitive density-dependent growth in a long-lived vertebrate after removal of nest predators

Examining the phenotypic and genetic underpinnings of life-history variation in long-lived organisms is central to the study of life-history evolution. Juvenile growth and survival are often density dependent in reptiles, and theory predicts the evolution of slow growth in response to low resources (resource-limiting hypothesis), such as under densely populated conditions. However, rapid growth is predicted when exceeding some critical body size reduces the risk of mortality (mortality hypothesis). Here we present results of paired, large-scale, five-year field experiments to identify causes of variation in individual growth and survival rates of an Australian turtle (Emydura macquarii) prior to maturity. To distinguish between these competing hypotheses, we reduced nest predators in two populations and retained a control population to create variation in juvenile density by altering recruitment levels. We also conducted a complementary split-clutch field-transplant experiment to explore the impact of incubation temperature (25° or 30°C), nest predator level (low or high), and clutch size on juvenile growth and survival. Juveniles in high-recruitment (predator removal) populations were not resource limited, growing more rapidly than young turtles in the control populations. Our experiments also revealed a remarkably long-term impact of the thermal conditions experienced during embryonic development on growth of turtles prior to maturity. Moreover, this thermal effect was manifested in turtles approaching maturity, rather than in turtles closer to hatching, and was dependent on population density in the post-hatching rearing environment. This apparent phenotypic plasticity in growth complements our observation of a strong, positive genetic correlation between individual body size in the experimental and control populations over the first five years of life (rG +0.77). Thus, these Australian pleurodiran turtles have the impressive capacity to acclimate plastically to major demographic perturbations and enjoy the longer-term potential to evolve adaptively to maintain viability

Past and future potential range changes in one of the last large vertebrates of the Australian continent, the emu Dromaius novaehollandiae

In Australia, significant shifts in species distribution have occurred with the loss of megafauna, changes in indigenous Australian fire regime and land-use changes with European settlement. The emu, one of the last megafaunal species in Australia, has likely undergone substantial distribution changes, particularly near the east coast of Australia where urbanisation is extensive and some populations have declined. We modelled emu distribution across the continental mainland and across the Great Dividing Range region (GDR) of eastern Australia, under historical, present and future climates. We predicted shifts in emu distribution using ensemble modelling, hindcasting and forecasting distribution from current emu occurrence data. Emus have expanded their range northward into central Australia over the 6000 years modelled here. Areas west of the GDR have become more suitable since the mid-Holocene, which was unsuitable then due to high precipitation seasonality. However, the east coast of Australia has become climatically sub-optimal and will remain so for at least 50 years. The north east of NSW encompasses the range of the only listed endangered population, which now occurs at the margins of optimal climatic conditions for emus. Being at the fringe of suitable climatic conditions may put this population at higher risk of further decline from non-climatic anthropogenic disturbances e.g. depredation by introduced foxes and pigs. The limited scientific knowledge about wild emu ecology and biology currently available limits our ability to quantify these risks

Developmental asynchrony might not reduce fitness in early life in painted turtles

Synchronous hatching and emergence of turtles from nests may be adaptive in predator avoidance during dispersal. However, little is known about the phenotypic consequences of such synchrony or the generality of predator avoidance in driving the evolution of this trait. Colbert et al. (2010) found that less advanced embryos hatched early in the presence of more advanced sibs, sustaining a persistent reduction in neuromuscular function. In this study, we experimentally assessed the influence of such accelerated embryonic development on hatching success, winter survival, and survival during terrestrial dispersal from the nest. Although we predicted that shortened incubation periods would reduce survival, early-hatching individuals suffered no detectable fitness costs at any stage considered in this study. Incubation temperature did not affect hatching success, and offspring sex did not affect survival across treatment groups. Incubation regime influenced offspring body size and was negatively correlated with dispersal time, however, there was no effect on survival during winter or terrestrial dispersal. Lack of a detectable fitness cost in these key early-life stages associated with hatching synchrony is consistent with a single, predator avoidance origin for this trait and retention in C. picta and other derived turtles via phylogenetic inertia

Nesting ecology and offspring recruitment in a long-lived turtle

The role of early life stages (eggs, neonates, and juveniles) for population persistence in long-lived organisms is thought to be minor. However, few long-term data sets are available to test this assumption. Variation in vital rates over space and time and the potential for the success of early life stages to shape adult reproductive behavior evolutionarily suggest that more thorough consideration of these life stages is necessary. In particular, the impact of climatic variation on early life-stage recruitment is not well understood. Furthermore, predation occupies a significant role in theoretical models of population dynamics, but its impact on populations through variable vital rates of early life stages is unknown. Maternal nest-site choice, an important component of nesting ecology, may influence many offspring traits and respond to selection to optimize offspring success. Overall, we have limited information regarding the long-term patterns of natural fluctuations in the nesting ecology and hatchling recruitment of populations of long-lived organisms. The research site for this ongoing long-term project is on an island in the Mississippi River near Thomson, Illinois, USA. Painted turtles (Chrysemys picta) have been studied extensively at this location since 1989 to examine the ecology and potential demographic consequences of nest-site choice and depredation, with the aim of understanding the evolution of maternal nesting behavior and its effects on offspring phenotype. We monitored the site every day of the nesting season each year to record nesting and depredation events. The data presented here include nesting phenology, nest vegetation cover, total number of nesting events, clutch size, depredation, and hatchling survival. Portions of this data set have been used to address related questions in ecology and evolutionary biology. In particular, climatic variation influences the probability of nest depredation events. Such events are typically nonrandom, primarily occurring adjacent to habitat edges. Because habitat edges may have atypical vegetation composition and vegetation influences nest temperature, such nonrandom depredation could influence offspring recruitment and, hence, population structure. Given the unique scope and accessibility of this data set, researchers and teachers should find it to be a valuable empirical resource for exploring important facets of nesting ecology and hatchling recruitment in a wild population of a long-lived species

Next Generation Advanced Video Guidance Sensor: Low Risk Rendezvous and Docking Sensor

The Next Generation Advanced Video Guidance Sensor (NGAVGS) is being built and tested at MSFC. This paper provides an overview of current work on the NGAVGS, a summary of the video guidance heritage, and the AVGS performance on the Orbital Express mission. This paper also provides a discussion of applications to ISS cargo delivery vehicles, CEV, and future lunar applications

An in silico performance characterization of respiratory motion guided 4DCT for high-quality low-dose lung cancer imaging.

This work aims to characterize the performance of an improved 4DCT technique aiming to overcome irregular breathing-related image artifacts. To address this, we have developed respiratory motion guided (RMG) 4DCT, which uses real-time breathing motion analysis to prospectively gate scans based on detection of irregular breathing. This is the first investigation of RMG-4DCT using a real-time software prototype, testing the hypothesis that it can reduce breathing irregularities during imaging, reduce image oversampling and improve image quality compared to a 'conventional' 4DCT protocol without breathing guidance. RMG-4DCT scans were simulated based on 100+  hours of breathing motion acquired for 20 lung cancer patients. Scan performance was quantified in terms of the beam on time (a surrogate for imaging dose), total scan time and the breathing irregularity during imaging (via RMSE of the breathing motion during acquisition). A conventional 4DCT protocol was also implemented using the same software prototype for a direct comparator to the RMG-4DCT results. We investigated the impact of key RMG-4DCT parameters such as gating tolerance, gantry rotation time and the use of baseline drift correction. Using a representative set of algorithm parameters, RMG-4DCT achieved significant mean reductions in estimated imaging dose (-17.8%, p  <  0.001) and breathing RMSE during imaging (-12.6%, p  <  0.001) compared to conventional 4DCT. These improvements came with increased scan times, roughly doubled on average (104%, p  <  0.001). Image quality simulations were performed using the deformable digital XCAT phantom, with image quality quantified based on the normalized cross correlation (NCC) between axial slices. RMG-4DCT demonstrated qualitative image quality improvements for three out of 10 phase bins, however the improvement was not significant across all 10 phases (p  =  0.08) at a population level. In choosing RMG-4DCT scan parameters, the trade-off between gating sensitivity and scan time may be optimized, demonstrating potential for RMG-4DCT as a viable pathway to improve clinical 4DCT imaging

Changes in participant behaviour and attitudes are associated with knowledge and skills gained by using a turtle conservation citizen science app

1. Citizen science has become a popular way to collect biodiversity data and engage the wider public in scientific research. It has the potential to improve the knowledge and skills of participants, and positively change their behaviour and attitude towards the environment. Citizen science outcomes are particularly valuable for wildlife conservation, as they could help alleviate human impacts on the environment. 2. We used an online questionnaire to investigate the consequences of participating in an Australian turtle mapping app, TurtleSAT, on skills and knowledge gain, and test for any association between these gains and behavioural or attitudinal changes reported by the participants. 3. One hundred and forty-eight citizen scientists completed our questionnaire, mostly from the states of New South Wales and Victoria. TurtleSAT was the third most common source of correct answers about turtle ecology and conservation, after a talk about turtles and personal observations/research. Citizen scientists who participated more often were more knowledgeable about turtles than infrequent users. Self-reported gains in knowledge and skills were positively linked to attitudinal and behavioural changes, such as being more aware of turtles on roads. However, behaviour and attitude changes were not related to participation rate. Respondents also reported that after learning about the current decline in turtle populations, they adopted several turtle-friendly practices, such as habitat restoration or moving turtles out of harm's way, underlining the importance of increasing people's awareness on species declines. 4. The reported changes in attitudes and behaviours are likely to positively impact the conservation of Australian freshwater turtles. Engagement with citizen science projects like TurtleSAT may result in participants being more interested in the natural world, by learning more about it and being more exposed to it, and therefore contributing more actively to its protection

A conserved Polϵ binding module in Ctf18-RFC is required for S-phase checkpoint activation downstream of Mec1

Defects during chromosome replication in eukaryotes activate a signaling pathway called the S-phase checkpoint, which produces a multifaceted response that preserves genome integrity at stalled DNA replication forks. Work with budding yeast showed that the ‘alternative clamp loader’ known as Ctf18-RFC acts by an unknown mechanism to activate the checkpoint kinase Rad53, which then mediates much of the checkpoint response. Here we show that budding yeast Ctf18-RFC associates with DNA polymerase epsilon, via an evolutionarily conserved ‘Pol ϵ binding module’ in Ctf18-RFC that is produced by interaction of the carboxyl terminus of Ctf18 with the Ctf8 and Dcc1 subunits. Mutations at the end of Ctf18 disrupt the integrity of the Pol ϵ binding module and block the S-phase checkpoint pathway, downstream of the Mec1 kinase that is the budding yeast orthologue of mammalian ATR. Similar defects in checkpoint activation are produced by mutations that displace Pol ϵ from the replisome. These findings indicate that the association of Ctf18-RFC with Pol ϵ at defective replication forks is a key step in activation of the S-phase checkpoint

Scavenging by threatened turtles regulates freshwater ecosystem health during fish kills

Humans are increasing the frequency of fish kills by degrading freshwater ecosystems. Simultaneously, scavengers like freshwater turtles are declining globally, including in the Australian Murray–Darling Basin. Reduced scavenging may cause water quality problems impacting both ecosystems and humans. We used field and mesocosm experiments to test whether scavenging by turtles regulates water quality during simulated fish kills. In the field, we found that turtles were important scavengers of fish carrion. In mesocosms, turtles rapidly consumed carrion, and water quality in mesocosms with turtles returned to pre-fish kill levels faster than in turtle-free controls. Our experiments have important ecological implications, as they suggest that turtles are critical scavengers that regulate water quality in freshwater ecosystems. Recovery of turtle populations may be necessary to avoid the worsening of ecosystem health, particularly after fish kills, which would have devastating consequences for many freshwater species

Climate and predation dominate juvenile and adult recruitment in a turtle with temperature-dependent sex determination

Conditions experienced early in life can influence phenotypes in ecologically important ways, as exemplified by organisms with environmental sex determination. For organisms with temperature-dependent sex determination (TSD), variation in nest temperatures induces phenotypic variation that could impact population growth rates. In environments that vary over space and time, how does this variation influence key demographic parameters (cohort sex ratio and hatchling recruitment) in early life stages of populations exhibiting TSD? We leverage a 17-year data set on a population of painted turtles, Chrysemys picta, to investigate how spatial variation in nest vegetation cover and temporal variation in climate influence early life-history demography. We found that spatial variation in nest cover strongly influenced nest temperature and sex ratio, but was not correlated with clutch size, nest predation, total nest failure, or hatching success. Temporal variation in climate influenced percentage of total nest failure and cohort sex ratio, but not depredation rate, mean clutch size, or mean hatching success. Total hatchling recruitment in a year was influenced primarily by temporal variation in climate-independent factors, number of nests constructed, and depredation rate. Recruitment of female hatchlings was determined by stochastic variation in nest depredation and annual climate and also by the total nest production. Overall population demography depends more strongly on annual variation in climate and predation than it does on the intricacies of nest-specific biology. Finally, we demonstrate that recruitment of female hatchlings translates into recruitment of breeding females into the population, thus linking climate (and other) effects on early life stages to adult demographics