Jack, master or both? The invasive ladybird Harmonia axyridis performs better than a native coccinellid despite divergent trait plasticity

The plasticity of performance traits can promote the success of biological invasions and therefore, precisely estimating trait reaction norms can help to predict the establishment and persistence of introduced species in novel habitats. Most studies focus only on a reduced set of traits and rarely include trait variability that may be vital to predicting establishment success. Here, using a split-brood full-sib design, we acclimated the globally invasive ladybird Harmonia axyridis and a native co-occurring and competing species Cheilomenes lunata to cold, medium and warm temperature regimes, and measured critical thermal limits, life-history traits, and starvation resistance. We used the conceptual framework of “Jack, Master or both” to test predictions regarding performance differences of these two species. The native C. lunata had a higher thermal plasticity of starvation resistance and a higher upper thermal tolerance than H. axyridis. By contrast, H. axyridis had a higher performance than C. lunata for preoviposition period, fecundity and adult emergence from pupae. We combined trait responses, transport duration and propagule pressure to predict the size of the populations established in a novel site following cold, medium and warm scenarios. Although C. lunata initially had a higher performance than the invasive species during transport, more individuals of H. axyridis survived in all simulated environments due to the combined life-history responses, and in particular, higher fecundity. Despite an increased starvation mortality in the warm scenario, given a sufficient propagule size, H. axyridis successfully established. This study underscores how the combination and plasticity of multiple performance traits can strongly influence establishment potential of species introduced into novel environments.

Early life starvation has stronger intra-generational than transgenerational effects on key life-history traits and consumption measures in a sawfly

Resource availability during development shapes not only adult phenotype but also the phenotype of subsequent offspring. When resources are absent and periods of starvation occur in early life, such developmental stress often influences key life-history traits in a way that benefits individuals and their offspring when facing further bouts of starvation. Here we investigated the impacts of different starvation regimes during larval development on life-history traits and measures of consumption in the turnip sawfly, Athalia rosae (Hymenoptera: Tenthredinidae). We then assessed whether offspring of starved and non-starved parents differed in their own life-history if reared in conditions that either matched that of their parents or were a mismatch. Early life starvation effects were more pronounced within than across generations in A. rosae, with negative impacts on adult body mass and increases in developmental time, but no effects on adult longevity in either generation. We found some evidence of higher growth rates in larvae having experienced starvation, although this did not ameliorate the overall negative effect of larval starvation on adult size. However, further work is necessary to disentangle the effects of larval size and instar from those of starvation treatment. Finally, we found weak evidence for transgenerational effects on larval growth, with intra-generational larval starvation experience being more decisive for life-history traits. Our study demonstrates that intra-generational effects of starvation are stronger than transgenerational effects on life-history traits and consumption measures in A. rosae.

A question of scale: Replication and the effective evaluation of conservation interventions

Conservation interventions can keep critically endangered species from going extinct and stabilize threatened populations. The species-specific, case-by-case approaches and small sample sizes inherent to applied conservation measures are not well suited to scientific evaluations of outcomes. Debates about whether a method “works” become entrenched in a vote-counting framework. Furthermore, population-level replication is rare but necessary for disentangling the effects of an intervention from other drivers of population change. Turtle headstarting is a conservation tool that has attracted strong opinions but little robust data. Logistical limitations, such as those imposed by the long lives of turtles, have slowed experimental evaluation and constrained the use of replication or experimental controls. Headstarting project goals vary among projects and stakeholders, and success is not always explicitly defined. To facilitate robust evaluations, we provide direction for data collection and reporting to guide the application of conservation interventions in logistically challenging systems. We offer recommendations for standardized data collection that allow their valuable results to contribute to the development of best practices, regardless of the magnitude of the project. An evidence-based and collaborative approach will lead to improved program design and reporting, and will facilitate constructive evaluation of interventions both within and among conservation programs.

Dispersal depends on body condition and predation risk in the semi-aquatic insect, Notonecta undulata

Dispersal is the movement of organisms across space, which has important implications for ecological and evolutionary processes, including community composition and gene flow. Previous studies have demonstrated that dispersal is influenced by body condition; however, few studies have been able to separate the effects of body condition from correlated variables such as body size. Moreover, the results of these studies have been inconsistent with respect to the direction of the relationship between condition and dispersal. We examined whether body condition influences dispersal in backswimmers (Notonecta undulata). We also tested whether an interaction between body condition and predation risk (another proximate factor that influences dispersal) could contribute to the previously observed inconsistent relationship between condition and dispersal. We imposed diet treatments on backswimmers in the laboratory, and measured the effects of food availability on body condition and dispersal in the field. We found that dispersal was a positive function of body condition, which may have important consequences for population characteristics such as the rate of gene flow and population growth. However, the effects of body condition and predation risk were additive, not interactive, and therefore, our data do not support the hypothesis that the interaction between condition and predation risk contributes to the inconsistency in the results of previous condition-dependent dispersal studies.

Sex-specific life history responses to nymphal diet quality and immune status in a field cricket

Individual fitness is expected to benefit from earlier maturation at a larger body size and higher body condition. However, poor nutritional quality or high prevalence of disease make this difficult because individuals either cannot acquire sufficient resources or must divert resources to other fitness-related traits such as immunity. Under such conditions, individuals are expected to mature later at a smaller body size and in poorer body condition. Moreover, the juvenile environment can also produce longer-term effects on adult fitness by causing shifts in resource allocation strategies that could alter investment in immune function and affect adult lifespan. We manipulated diet quality and immune status of juvenile Texas field crickets, Gryllus texensis, to investigate how poor developmental conditions affect sex-specific investment in fitness-related traits. As predicted, a poor juvenile diet was related to smaller mass and body size at eclosion in both sexes. However, our results also reveal sexually dimorphic responses to different facets of the rearing environment: female life history decisions are affected more by diet quality, whereas males are affected more by immune status. We suggest that females respond to decreased nutritional income because this threatens their ability to achieve a large adult body size, whereas male fitness is more dependent on reaching adulthood and so they invest in immunity and survival to eclosion.

You are what you eat: food limitation affects reproductive fitness in a sexually cannibalistic praying mantid

Resource limitation during the juvenile stages frequently results in developmental delays and reduced size at maturity, and dietary restriction during adulthood can affect longevity and reproductive output. Variation in food intake can also result in alteration to the normal pattern of resource allocation among body parts or life-history stages. My primary aim in this study was to determine how varying juvenile and/or adult feeding regimes affect particular female and male traits in the sexually cannibalistic praying mantid Pseudomantis albofimbriata. Praying mantids are sit-and-wait predators whose resource intake can vary dramatically depending on environmental conditions within and across seasons, making them useful for studying the effects of feeding regime on various facets of reproductive fitness. In this study, there was a significant trend/difference in development and morphology for males and females as a result of juvenile feeding treatment, however, its effect on the fitness components measured for males was much greater than on those measured for females. Food-limited males were less likely to find a female during field enclosure experiments and smaller males were slower at finding a female in field-based experiments, providing some of the first empirical evidence of a large male size advantage for scrambling males. Only adult food limitation affected female fecundity, and the ability of a female to chemically attract males was also most notably affected by adult feeding regime (although juvenile food limitation did play a role). Furthermore, the significant difference/trend in all male traits and the lack of difference in male trait ratios between treatments suggests a proportional distribution of resources and, therefore, no trait conservation by food-limited males. This study provides evidence that males and females are under different selective pressures with respect to resource acquisition and is also one of very few to show an effect of juvenile food quantity on adult reproductive fitness in a hemimetabolous insect.

A comparative study on effects of normal versus elevated temperatures during preimaginal and young adult period on body weight and fat body content of mature Coccinella septempunctata and Harmonia axyridis (Coleoptera: Coccinellidae)

Two climate chamber experiments were performed to simulate the effects of global warming on life table parameters of coccinellids. We investigated the effects of two daily temperature profiles during preimaginal development (larval and pupal) and the young adult period (first 10 d) on body weight and fat body content of adult Coccinella septempunctata L. and Harmonia axyridis (Pallas) fed English grain aphids [Sitobion avenae (F.)] ad libitum: 1) normal, i.e., current daily temperatures in central Europe (T0: mean, 17.8°C; maximum, 21.8°C; minimum, 13.4°C) and 2) increased by 3K (T3: mean, 20.8°C; maximum, 25.5°C; minimum, 15.7°C). The first experiment was performed at the same temperatures (T0 or T3) during both periods to establish the responses of the two species to temperature. The second was conducted to identify the period (preimaginal or adult) in which the responses occurred and to confirm the results of the first experiment. Compared with normal temperatures (T0), elevated temperatures (T3) resulted in significant decreases in preimaginal development time and increases in aphid consumption rates in both species. C. septempunctata (10-d-old adults) had the highest weights when reared at T3, H. axyridis at T0. C. septempunctata was significantly heavier than H. axyridis in most cases, particularly in females. The body fat content of C. septempunctata was higher than that of H. axyridis at T0 and T3 temperatures. At T3 temperatures, fat accumulation in C. septempunctata increased, whereas that in H. axyridis remained relatively low. Body weight and fat body content of 10-d-old adults of both species seemed to be determined by temperature conditions during preimaginal development.

The effects of larval nutrition on reproductive performance in a food-limited adult environment

It is often assumed that larval food stress reduces lifetime fitness regardless of the conditions subsequently faced by adults. However, according to the environment-matching hypothesis, a plastic developmental response to poor nutrition results in an adult phenotype that is better adapted to restricted food conditions than one having developed in high food conditions. Such a strategy might evolve when current conditions are a reliable predictor of future conditions. To test this hypothesis, we assessed the effects of larval food conditions (low, improving and high food) on reproductive fitness in both low and high food adults environments. Contrary to this hypothesis, we found no evidence that food restriction in larval ladybird beetles produced adults that were better suited to continuing food stress. In fact, reproductive rate was invariably lower in females that were reared at low food, regardless of whether adults were well fed or food stressed. Juveniles that encountered improving conditions during the larval stage compensated for delayed growth by accelerating subsequent growth, and thus showed no evidence of a reduced reproductive rate. However, these same individuals lost more mass during the period of starvation in adults, which indicates that accelerated growth results in an increased risk of starvation during subsequent periods of food stress.