Integrative and Comparative Biology最新文献

Ecological specialization is often described as an evolutionarily tenuous, or dead-end, strategy, where the loss of one partner may be catastrophic for the other. Some of the most highly specialized interactions are brood-pollination mutualisms, wherein plants trade food and shelter for pollination services, often at the cost of some offspring (i.e., fertile seeds). With few exceptions, brood-pollination mutualisms are generally obligate, thus the reproduction of both plant and insect pollinator are interdependent and cannot occur without the other. In many cases, these interactions are also species-specific and pairwise. Due to the severity of reproductive constraint, an evolutionary "dead-end" seems all but inevitable. However, host-shifts are remarkably common, even in brood-pollination mutualisms, and may enhance evolutionary resilience. Yet, we still lack a clear understanding of mechanisms of insect localization and choice of a new host-plant in these highly specialized mutualisms. Recently, Rhopalotria furfuracea, the specialized brood-site pollinator of the cycad Zamia furfuracea, has been observed on other Zamia species in an artificial environment (i.e., a conservation garden) where it is not found in the wild. To better understand what cues are facilitating this shift, we consider both "private channels", or unique secondary metabolites thought to facilitate partner fidelity in ecologically specialized interactions, and the more general cue humidity, representing 2 modes of signaling for which the ecological importance has been previously described in the R. furfuracea-Z. furfuracea mutualism. We hypothesize that humidity will increase pollinator attraction to non-host plant scent. To test this, we characterize via gas chromatography mass spectrometry the previously unreported scent of the non-host plant, Z. paucijuga, that R. furfuracea has recently colonized and find that it qualitatively differs from that of Z. furfuracea. Behavior trials, consisting of 2-way y-tube olfactometer choice assays find that weevils are repelled by the non-host plant volatile blend, but that the addition of humidity overcomes avoidance behavior, suggesting that less specialized traits, such as primary metabolites, may create opportunities for novel associations to develop over evolutionary time.

The Western honey bee (Apis mellifera L.) has been managed by humans for centuries for honey, wax, and most recently, crop pollination. The deep history of human association with this species has enabled agricultural practices that reduce biodiversity of pollinating wild bees, largely through habitat modification. However, there is also interest in determining if A. mellifera presence itself contributes significantly to wild bee population declines. Here, we review the evidence of A. mellifera effects on wild bees, with a particular emphasis on critically evaluating the evidence for detrimental impacts associated with resource competition. Despite accelerated research in this area, only ∼13% of resource competition studies evaluated fitness effects of A. mellifera on wild bees, a research gap that has persisted for over 20 years. About three times as many studies have evaluated effects of A. mellifera on wild bee community parameters, including wild bee abundance, which provides a measure of a landscape's "bee carrying capacity." Just over 20% of these studies show a negative correlation with A. mellifera abundance. In a novel analysis of 68 additional studies measuring bee communities for a variety of other reasons, we found negative correlations between A. mellifera abundance and any measure of the wild bee community (richness, abundance, etc.) for nine, and the measures showing A. mellifera impacts were varied. For example, only two of these studies showed negative correlations between A. mellifera and wild bee abundances. In contrast, we also found similar numbers of positive relationships between A. mellifera and various wild bee community parameters, including ten studies that showed positive relationships between A. mellifera and wild bee abundances. Most studies (64%) showed no relationship with any factor. We found no clear pattern to explain which habitat types are more vulnerable to A. mellifera competition, nor is the literature clear on impactful densities of managed hives in particular environment types. We discuss suggestions for future research, as well as ways the research community could clarify its conservation priorities with respect to resource competition. Resource competition between A. mellifera and wild bees is clearly a concern in some cases. However, more work is needed to identify and predict where A. mellifera poses a significant threat to wild bee populations. Overall, the data do not support a generalized and widespread negative relationship between A. mellifera abundance and wild bee community health. Rather, conservation measures that reliably improve wild bee health (habitat preservation and restoration) will likely have positive effects on A. mellifera, and vice versa.

Temperature is a major driver of individual performance in ectotherms, with this impact depending on stressor intensity and duration. Differences in individual response across temperature, time, and populations are shaped by the interplay between evolutionary adaptation and phenotypic plasticity. Some populations are able to thrive in novel and changing environments despite limited genetic diversity, raising the question of how plasticity and adaptation interact after significant genetic diversity loss. The European green crab (Carcinus maenas) is a textbook example of this phenomenon: invasive populations boast a broad thermal tolerance and exceptional thermal flexibility even after repeated genetic bottlenecks. Despite this loss of diversity overall, prior work has found a strong population-level association between variation at a specific extended genomic region (supergene), cold tolerance, and sea surface temperature. We conducted a series of three experiments using righting response to characterize sublethal thermal tolerance and plasticity in introduced green crab populations, then determined if these factors were associated with supergene genotype for individual adult crabs. Crabs showed signs of stress after exposure to a 30°C heat shock in one experiment. Interestingly, a second experiment exposing C. maenas to repeated 24-h heat shocks showed that prior heat shock conferred beneficial plasticity during a subsequent event. The third experiment examined cold acclimation over multiple timepoints up to 94 h. At 5°C, certain crabs exhibited an acclimatory response where righting slowed dramatically at first, and then gradually sped up after a longer period of cold exposure. Several crabs failed to right at 1.5°C, which could be indicative of dormancy employed to reduce energy consumption in colder conditions. There were no significant relationships between individual plasticity and supergene genotype in any experiment. Linking population-level genetic associations with individual-level physiology is complex, and reflects the impact of environmental conditions such as temperature throughout life history in shaping adult phenotype. Our results highlight the robust thermal tolerance and plasticity that adult green crabs maintain despite a substantial reduction in genetic diversity, and underscore the importance of probing population-level genotype-phenotype associations at the individual level.

Ectothermic species in lowland tropical forests have evolved in historically stable climates, leading to the prediction that transcriptomic and phenotypic plasticity do not play major roles in their responses to changes in environmental temperature. However, these species are often thermoconformers and are therefore exposed to short-term temporal fluctuations in temperature. Hence, transcriptomic plasticity in tropical forest ectotherms might replace behavioral thermoregulation as a mechanism to buffer against thermal stress. In particular, upregulation of heat shock proteins can occur during thermal stress in a range of organisms. However, while many studies have explored gene expression plasticity in response to heat stress in model organisms, little is known about transcriptomic plasticity in the tropical, non-model species that will be the most impacted by climate change. We studied the effects of moderate and severe acute heat stress events in the Panamanian slender anole (Anolis apletophallus) to gain insight into a mechanism that might allow tropical ectotherms to withstand the heat waves that are likely to rise in frequency over the coming decades under anthropogenic climate change. We found that multiple genes were upregulated across several heat shock protein networks in three tissues, and the magnitude of the expression response was similar irrespective of whether heat stress was moderate or severe. Overall, our results indicate a potentially crucial role for heat shock protein networks in the ability of tropical ectotherms to resist the negative effects of rising temperatures.

When animals compete over essential and limited resources, how they gather information about fighting ability is a crucial factor influencing their decision-making. Most research in animal contests asks how decisions are made when facing a single competitor; however, in many cases, individuals face multiple potential opponents and may incorporate information on this social environment. In addition, recent research suggests that animals perceive contest-relevant stimuli like body size in a proportional, not absolute, manner; this proportional processing has rarely, if ever, been incorporated into studies of contest assessment. Green swordtail fish (Xiphophorus hellerii) live in social aggregations, in which males may defend females from multiple potential opponents. Here, we asked how focal male green swordtails defended live females when presented with two simulated males that differed by known sizes. We found that focal males spent less time near the larger, more salient, of the two competitors as the mean size of both simulated competitors increased. That is, focal males mainly used information on the social environment to make competitive decisions, as opposed to information about own or relative fighting ability as commonly assumed in most contest theory. We also found that males who spent less time with the largest competitor shifted their attention to the defended female, devoting more time near this resource. Our findings suggest that, when there are multiple potential competitors, common models of decision-making in contests may be less applicable than previously assumed. Further, given the common use of proportional processing across animals, we suggest that future work on contests incorporates this type of perception.

Wind can significantly influence heat and water exchange between organisms and their environment, yet microclimatic variation in wind is often overlooked in models forecasting the effects of environmental change on organismal performance. Accounting for the effects of wind may become even more critical given the anticipated changes in wind speed across the planet as climates continue to warm. In this study, we first assessed how wind speed varies across the planet and how wind speed may change under climate warming at macroclimatic scales. We also used microclimatic data to assess how wind speed changes temporally throughout the day and year as well as the relationship between wind speed, temperature, and standard deviation in each environmental variable using data from weather stations in North America. Finally, we used a suite of biophysical simulations to understand how wind speed (and its interactions with other environmental variables and organismal traits) affects the temperatures and rates of water loss that plants and animals experience at a microclimatic scale. We found substantial latitudinal variation in wind speed and the change in wind speed under climate change, demonstrating that temperate regions are predicted to experience simultaneous warming and reductions in wind speed. From the microclimatic data, we also found that wind speed is positively associated with temperature and temperature variability, indicating that the effects of wind speed may become more challenging to predict under future warming scenarios. The biophysical simulations demonstrated that convective and evaporative cooling from wind interacts strongly with organismal traits (such as body size, solar absorptance, and conductance) and the heating effects of solar radiation to shape heat and water fluxes in terrestrial plants and animals. In many cases, the effect of wind (or its interaction with other variables) was comparable to the effects of air temperature or solar radiation. Understanding these effects will be important for predicting the ecological impacts of climate change and for explaining clinal variation in traits that have evolved across a range of thermal environments.

Climate change is leading to higher and more variable temperatures worldwide, and these changes are likely to have consequences on the incubation stage of egg-laying organisms. Artificial incubation can be used to address a variety of mechanistic, ecological, and conservation questions related to the development of egg-laying animals in a warming climate. Artificial incubation of passerine eggs remains rare because their eggs can be highly sensitive to incubation conditions, causing it to be challenging to successfully incubate their eggs to hatch in captivity. The goal of this study was to describe a protocol to artificially incubate eggs of house sparrows (Passer domesticus), a widespread model species, and to provide a framework that can be used to develop protocols for artificial incubation of other passerine species. Since sufficient egg mass loss is necessary for proper development and can be related to hatching success, we monitored mass loss of eggs in natural nests in the field and used this information to inform and modify artificial incubation conditions. We found that eggs in our study population lost an average of 11.34% of their original mass across the incubation period, and that mass loss was greater later in incubation. To identify conditions promoting high hatching success, we tested incubation conditions of 36.9-37.4°C, 40-50% relative humidity (RH), and automatic and hand egg turning. We achieved 100% hatching success of artificially incubated eggs using a rocking incubator with automatic turning (90°/h) and three 180°C hand turns per day, incubation conditions of 37.36°C and 42.6% RH, and hatching conditions of 36.73°C and 57.9% RH. These conditions and the framework we provide to develop incubation protocols for other passerine species can be applied to better understand how changing environmental conditions are affecting the development of egg-laying organisms.

Changing climatic conditions can lead to diminished overlap in the timing of flowering and pollinator foraging, potentially resulting in the weakening or loss of plant-pollinator interactions and reducing the fitness of both partners. However, several complexities of phenological shifts limit our ability to predict their consequences for plant-pollinator mutualisms. First, phenological shifts reflect the responses of individuals but are often summarized at the community, species, or population level, potentially obscuring variation that has important implications for interactions within and between species. Second, metrics of phenological asynchrony in pollination, such as temporal overlap between flowering and pollinator foraging, may not accurately characterize changes in interaction strength or fitness costs and benefits and thus are not true metrics of mismatch. Third, our focus has been on shifts in individual life-history events, such as flowering, rather than entire life cycles, despite the physiological integration of seasonal life-history stages (phenophases) that may be under different selection pressures. We suggest that we can advance our understanding of phenological shifts and their consequences for plants and pollinators by studying individual phenological variation in both partners across natural or experimental environmental gradients, measuring interaction rates and their fitness implications in addition to synchrony or overlap, and taking an integrated life cycle approach that can reveal trade-offs. Together, these approaches can yield temporally explicit fitness landscapes for plant and pollinator phenologies and improve our understanding of the consequences of climate change-induced phenological shifts.

The fitness implications of climate variability and change are often estimated by integrating an organism's thermal sensitivity of performance across a time series of experienced body temperatures. Although this approach is an important first step in evaluating an organism's sensitivity to climate or climate change, it ignores potential influences of recent exposure to thermal stress on current thermal sensitivity. Here, we account for recent thermal stress by estimating rates of damage, repair, and other carryover effects; and we illustrate the approach with fecundity and development rate data from experiments that exposed aphids to various stressful and fluctuating temperatures. Our analyses indicate that heat stress for these aphids starts near the upper thermal limit for performance; that heat stress intensifies with both the exposure duration and with temperature; and that there is considerable capacity for repair at temperatures near the thermal optimum for performance. Results from experiments with aphids indicate that incorporating time series of damage, recovery, and repair will be necessary to anticipate fitness outcomes of climate change and variability.

Plant-pollinator interactions have persisted and evolved over millions of years. These interactions are shaped by environmental factors. However, global environmental changes are disturbing these interactions in the Anthropocene. One way both plants and pollinators can respond (and potentially adapt) to these changing environments is through phenotypic plasticity mediated by epigenetic modifications and non-genetic inheritance. Yet, research on how, and to what extent, epigenetic modifications and non-genetic inheritance shape plant-pollinator dynamics is rare. In this forward-looking perspective, we discuss different ways in which the environment mediates epigenetic marks and non-genetic inheritance into the subsequent generation. By taking a broader perspective, we discuss four mechanisms of epigenetic modification and non-genetic inheritance in both plants and pollinator systems: epigenetic modifications, inter-generational non-genetic inheritance, transgenerational non-genetic inheritance, and cultural transmission. We discuss the roles of various epigenetic marks and the transfer of molecules that cause epigenetic changes and non-genetic inheritance in plants and pollinators, which either directly or indirectly affect the outcome of plant-pollinator interactions. We provide a framework for the ecological and evolutionary implications for inheritance of acquired traits driving plant-pollinator interactions and discuss its importance in a rapidly changing environment. Lastly, we suggest ways to experimentally test the role of epigenetic marks and non-genetic inheritance, and how to integrate such mechanisms into long-term studies on plant-pollinator interactions during the Anthropocene.