No abstract

Flying endothermic insects thermoregulate, likely to improve flight performance. Males of the Sonoran Desert bee, Centris caesalpiniae Cockerell, seek females at aggregations beginning at sunrise and cease flight near midday when air temperature peaks. To identify the thermoregulatory mechanisms for C. caesalpiniae males, we measured tagma temperatures, wingbeat frequency, water loss rates, metabolic rates, and tagma masses of flying bees across shaded air temperatures of 19 to 38°C. Surface area, wet mass, and dry mass declined with air temperature, suggesting that individual bees do not persist for the entire morning. The largest bees may be associated with cool, early mornings because they are best able to warm themselves and/or because they run the risk of overheating in the hot afternoons. Thorax temperatures were high (38 to 45°C) and were moderately well-regulated, while head and abdomen temperatures were cooler and less controlled. The abdominal temperature excess ratio increased as air temperature rose, indicating active heat transfer from the pubescent thorax to the relatively bare abdomen with warming. Mass-specific metabolic rate increased with time, air, and thorax temperatures, but wingbeat frequency did not vary. Mass-specific water loss rate increased with air temperature, but this was a minor mechanism of thermoregulation. Using a heat budget model, we showed that whole-body convective conductance more than doubled through the morning, providing strong evidence that the primary mechanism of regulating thorax temperature during flight for these bees is increased use of the abdomen as a convector at higher air temperatures.

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Historical data suggest that many bee species have declined in body size. Larger-bodied bees with narrow phenological and dietary breadth are most prone to declines in body size over time. This may be especially true in solitary, desert-adapted species that are vulnerable to climate change such as Centris pallida (Hymenoptera: Apidae). In addition, body size changes in species with size-linked behaviours could threaten the prevalence of certain behavioural phenotypes long-term. C. pallida solitary bees are found in the Sonoran Desert. Males use alternative reproductive tactics (ARTs) and are dimorphic in both morphology and behaviour. C. pallida male body size has been studied since the 1970s in the same population. The authors collected body size data in 2022 and combined it with published records from 1974-2022. The authors find a persistent decline in the mean head width of patrolling males, and shifts towards smaller body sizes in the populations of males found foraging and hovering. Both morphs declined in average body size, and the proportion of large-morph males in the population decreased by 8%.Mating males did not decline in mean body size over the last five decades. The authors discuss hypotheses related to the decline in C. pallida male head width. Finally, the authors advocate for C. pallida as an excellent study system for understanding the stability of ARTs with size-linked behavioural phenotypes.

Historical data suggest that many bee species have declined in body size. Larger-bodied bees with narrow phenological and dietary breadth are most prone to declines in body size over time. This may be especially true in solitary, desert-adapted species that are vulnerable to climate change – such as Centris pallida (Hymenoptera: Apidae). In addition, body size changes in species with size-linked behaviors could threaten the prevalence of certain behavioral phenotypes long-term. C. pallida solitary bees are found in the Sonoran Desert. Males use alternative reproductive tactics (ARTs) and are dimorphic in both morphology and behavior. C. pallida male body size has been studied since the 1970s in the same population. We collected body size data in 2022 and combined it with published records from 1974-2022. We find a persistent decline in the mean head width of patrolling males, and shifts towards smaller body sizes in the populations of males found foraging and hovering. Mating males did not experience a decline in mean body size over time. We discuss hypotheses related to the decline in C. pallida male head width. Finally, we advocate for C. pallida as an excellent study system for understanding the stability of ARTs with size-linked behavioral phenotypes.

No abstract

Parasitic diseases caused by kinetoplastid parasites of the genera Trypanosoma and Leishmania are an urgent public health crisis in the developing world. These closely related species possess a number of multimeric enzymes in highly conserved pathways involved in vital functions, such as redox homeostasis and nucleotide synthesis. Computational alanine scanning of these protein-protein interfaces has revealed a host of potentially ligandable sites on several established and emerging anti-parasitic drug targets. Analysis of interfaces with multiple clustered hotspots has suggested several potentially inhibitable protein-protein interactions that may have been overlooked by previous large-scale analyses focusing solely on secondary structure. These protein-protein interactions provide a promising lead for the development of new peptide and macrocycle inhibitors of these enzymes.

It is advantageous for flying insects to be functional across a range of temperatures when competing for mates; breadth of performance can arise from broad tolerance or thermoregulation. Tactics of flying insects typically include moving hot hemolymph from the thorax to cooler body segments, evaporative water loss, and changes in metabolic heat production. For dimorphic Centris caesalpiniae male bees, the large morphs dig for females at ground‐level, flying infrequently, whereas the small morph hovers and flies. At a mate‐aggregation site, air temperature varied from 17 ºC to 37 ºC across and within days; operative temperatures of metanders reached 50 ºC on the ground when mating activity ceased, suggesting that high temperatures and radiation constrain the mating period, and that C. caesalpiniae's upper thermal tolerance is high, but not exceptional. These bees exhibited modest thermoregulation of thorax and head temperatures, with segment temperatures increasing 0.5‐0.6 ºC per ºC air temperature both on the ground and in flight. During flight, evaporative water loss and heat movement to the abdomen contributed to thermoregulation. On the ground, bees moved hemolymph to the head. These results suggest bees thermoregulate the thorax to improve flight performance. Metabolic water production was about half of water loss rates and metanders lose about 17% of their body water per hour during flight. No one has observed metanders feeding or drinking, and several hours of flight would presumably cause a lethal loss of body water. While we currently lack information on the duration of activity of individuals, it is possible that thermoregulatory water loss may constrain the activity of metanders.