When Landscape Ecology Meets Physiology: Effects of Habitat Fragmentation on Resource Allocation Trade-Offs

Landscape heterogeneity is a general feature of natural environments, strongly affected by habitat fragmentation. It can affect a population's dynamics and probability of extinction. Fragmentation increases among-patch isolation and decreases patch size, resulting in a reduction in available resources in smaller patches. To persist, animals must be able to translate the variation imposed by fragmentation into adaptive energy allocation strategies that enable populations to avoid extinction. This means that physiological adaptations are expected to reflect changes in landscape configuration, especially in the size of the natural habitat patches and degree of isolation among them. We propose a novel, integrative conceptual framework in which spatial characteristics of the environment, imposed by fragmentation, lead to specific life-history traits that increase survival (at the individual level) and decrease the likelihood of extinction (as an emergent property at the population level). We predict that a resource allocation trade-off between the life-history traits of reproduction and dispersal along a fragmentation gradient will emerge. Populations occurring in patches of different sizes and isolations along gradients of fragmentation and productivity will exhibit differences in the strength of the dispersal-reproduction trade-off. Emerging from this framework are several explicit and testable hypotheses that predict that the dispersal-reproduction trade-off will be shaped by landscape heterogeneity imposed by fragmentation. Hence, this trade-off serves as the mechanistic link that translates environmental variation created by fragmentation into variation in species abundances and population dynamics by lowering local extinction probability and increasing overall population persistence

An Herbivore’s Thermal Tolerance is Higher Than That of the Ant Defenders in a Desert Protection Mutualism

In North American deserts, many species of cactus attract ants to their extrafloral nectaries; the ants actively defend the food source, and hence the plant, against herbivores. In thermally extreme environments, however, networks of positive and negative interactions like these are likely to be sensitive to the thermal limitations of each of the interacting species. We compared the thermal tolerance of a common phytophagous cactus bug, Narnia pallidicornis (Hemiptera: Coreidae), to that of the ants that defend the cactus Ferocactus wislizeni in the Sonoran Desert, USA. We used flow-through respirometry to experimentally determine the thermal limit of the herbivore and compared this to the thermal limits of the ant defenders, determined previously. In the field, we recorded herbivore frequency (proportion of plants with N. pallidicornis) and abundance (the number of N. pallidicornis per plant) in relation to ambient temperature, ant species presence and identity, and fruit production. We show that N. pallidicornis has a higher thermal tolerance than the four most common ant mutualists, and in the laboratory can survive very high temperatures, up to 43°C. Herbivore frequency and abundance in the field were not related to the daily high temperatures observed. Plants that were not defended by ants were occupied by more N. pallidicornis, although they showed no reduction in fruit set. Therefore, herbivory is likely to continue on fishhook barrel cacti even at high temperatures, especially those temperatures beyond the thermal tolerance of the ant defenders. The consequences of increased herbivory, however, remain unclear. Mutualisms are essential for ecosystem functioning; it is important to understand the thermal sensitivity of these interactions, especially in light of expected increases in global temperature regimes

An empirical test of the relationship between environmental variability and phenotypic plasticity in the pallid-winged grasshopper (Trimerotropis pallidipennis)

Phenotypic plasticity has been proposed as an adaptive mechanism by which organisms can maximize their fitness in response to short-term environmental variability. In this dissertation, I test one prediction that comes out of this idea: that populations from more variable environments should have higher levels of phenotypic plasticity than populations from less variable environments. I first analyzed precipitation variability and predictability across nine biomes in the Southwestern U.S. to determine a gradient of environmental variability. There was a non-linear negative relationship between precipitation variability and precipitation mean. In general, contrary to common belief, desert biomes were no more variable nor less predictable than nondesert biomes. I tested the relationship between environmental variability and phenotypic plasticity in seven populations of the pallid-winged grasshopper (Trimerotropis pallidipennis). Contrary to prediction, populations from more variable environments had lower, not higher, levels of phenotypic plasticity in development time. There was a significant convex quadratic relationship between plasticity for size at maturity and precipitation variability. In general, females in populations with more plasticity in development time had lower fitness. Plasticity in size at maturity generally did not affect fecundity, but increased survivorship. Plasticities in both traits conferred no significant costs or benefits in males. I tested the hypothesis that these results were due to constraints on the evolution of plasticity: either to a lack of genetic variation for plasticity or to antagonistic pleiotropy between size at maturity and development time. I found sufficient genetic variation for plasticity to evolve in all study populations and little evidence for antagonistic pleiotropy. I further tested whether selection for developmental stability or directional selection for short development time could explain the pattern of plasticity responses across the gradient. Low plasticity responses were apparently due to selection for developmental stability in deserts. I found weak evidence that antagonistic and synergistic selection could also explain the plasticity responses. I found no evidence that directional selection for short development time in all environments could explain the lower levels of phenotypic plasticity in the desert populations

The adaptive role of melanin plasticity in thermally variable environments

Understanding the evolution of adaptive plasticity is fundamental to our knowledge of how organisms interact with their environments and cope with environmental change. Plasticity in melanin pigmentation is common in response to variable environments, especially thermal environments. Yet, the adaptive significance of melanin plasticity in thermally variable environments is often assumed, but rarely explicitly tested. Furthermore, understanding the role of plasticity when a trait is responsive to multiple environmental stimuli and plays many functional roles remains poorly understood. We test the hypothesis that melanin plasticity is an adaptation for thermally variable environments using Hyles lineata, the white-lined sphinx moth, which shows plasticity in melanin pigmentation during the larval stage. Melanin pigmentation influences thermal traits in H. lineata, as melanic individuals had higher heating rates and reached higher body temperatures than non-melanic individuals. Importantly, melanin pigmentation has temperature specific fitness consequences. While melanic individuals had an advantage in cold temperatures, neither phenotype had a clear fitness advantage at warm temperatures. Thus, the costs associated with melanin production may be unrelated to thermal context. Our results highlight the importance of explicitly testing the adaptive role of plasticity and considering all the factors that influence costs and benefits of plastic phenotypes across environments.12 month embargo; first published 02 November 2023This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

data for Fig 7 photogate and 20E

Timing of photoperiodic gate for PTTH secretion and ecdysone secretion, as in Figure 7

Within-host competition drives energy allocation trade-offs in an insect parasitoid

Organismal body size is an important biological trait that has broad impacts across scales of biological organization, from cells to ecosystems. Size is also deeply embedded in life history theory, as the size of an individual is one factor that governs the amount of available resources an individual is able to allocate to different structures and systems. A large body of work examining resource allocation across body sizes (allometry) has demonstrated patterns of allocation to different organismal systems and morphologies, and extrapolated rules governing biological structure and organization. However, the full scope of evolutionary and ecological ramifications of these patterns have yet to be realized. Here, we show that density-dependent larval competition in a natural population of insect parasitoids (Drino rhoeo: Tachinidae) results in a wide range of body sizes (largest flies are more than six times larger (by mass) than the smallest flies). We describe strong patterns of trade-offs between different body structures linked to dispersal and reproduction that point to life history strategies that differ between both males and females and individuals of different sizes. By better understanding the mechanisms that generate natural variation in body size and subsequent effects on the evolution of life history strategies, we gain better insight into the evolutionary and ecological impacts of insect parasitoids in tri-trophic systems.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

All lines

Response to selection of all lines for body size, development time, critical weight, interval to cessation of growth and growth rate

Sex differences in the utilization of essential and non-essential amino acids in Lepidoptera

The different reproductive strategies of males and females underlie differences in behavior that may also lead to differences in nutrient use between the two sexes. We studied sex differences in the utilization of two essential amino acids (EAAs) and one non-essential amino acid (NEAA) by the Carolina sphinx moth (Manduca sexta). On day one post-eclosion from the pupae, adult male moths oxidized greater amounts of larva-derived AAs than females, and more nectar-derived AAs after feeding. After 4 days of starvation, the opposite pattern was observed: adult females oxidized more larva- derived AAs than males. Adult males allocated comparatively small amounts of nectar-derived AAs to their first spermatophore, but this allocation increased substantially in the second and third spermatophores. Males allocated significantly more adult-derived AAs to their flight muscle than females. These outcomes indicate that adult male and female moths employ different strategies for allocation and oxidation of dietary AAs.National Science Foundation USA [IOS-1053318]12 month embargo; published: 1 August 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Data for Fig F1 directions of selection

Directions of selection- short and long development time and antagonistic and synergistic directions of selection, as in Figure F1