Physiological and Biochemical Zoology最新文献

AbstractLaboratory animal models have shown that blood serotonin levels reflect consistent individual differences in behavioral decision-making and maternal behavior. Serotonin could also help to understand intraspecific variation in reproductive strategies, although the mechanisms are poorly understood. In this study, the relationships of plasma serotonin with breeding parameters and parental behavior were examined in wild great tits (Parus major). Females who laid eggs earlier had higher levels of serotonin in the second half of the nestling period, while no significant relationship of serotonin with clutch size, brood size, and body size was detected. In males, serotonin levels were negatively related to clutch size and brood size and positively related to body size. The association of serotonin with provisioning behavior was sex specific, and acute fear stress induced by a predator presentation did not change this relationship. Food provisioning was positively related to size-corrected serotonin levels in females and negatively related to size-corrected serotonin levels in males. These results suggest that peripheral serotonin is a sensitive marker of parental behavior and reproductive effort in wild birds, while the mechanisms linking this neurotransmitter to reproduction are probably mediated by interplay between the serotonergic system, sex hormones, and other neurotransmitters.

AbstractKrogh's principle states, "For such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied." The downside of picking a question first and then finding an ideal organism on which to study it is that it will inevitably leave many organisms neglected. Here, we promote the inverse Krogh principle: all organisms are worthy of study. The inverse Krogh principle and the Krogh principle are not opposites. Rather, the inverse Krogh principle emphasizes a different starting point for research: start with a biological unit, such as an organism, clade, or specific organism trait, then seek or create tractable research questions. Even the hardest-to-study species have research questions that can be asked of them: Where does it fall within the tree of life? What resources does it need to survive and reproduce? How does it differ from close relatives? Does it have unique adaptations? The Krogh and inverse Krogh approaches are complementary, and many research programs naturally include both. Other considerations for picking a study species include extreme species, species informative for phylogenetic analyses, and the creation of models when a suitable species does not exist. The inverse Krogh principle also has pitfalls. A scientist that picks the organism first might choose a research question not really suited to the organism, and funding agencies rarely fund organism-centered grant proposals. The inverse Krogh principle does not call for all organisms to receive the same amount of research attention. As knowledge continues to accumulate, some organisms-models-will inevitably have more known about them than others. Rather, it urges a broader search across organismal diversity to find sources of inspiration for research questions and the motivation needed to pursue them.

AbstractLocomotion is a defining characteristic that can dictate many aspects of an organism's life history in the pursuit of maximizing fitness, including escaping predators, capturing prey, and transitioning between habitats. Exhaustive exercise can have negative consequences for both short-term and long-term energetics and life history trade-offs, influencing fish survival and reproduction. Studies of swimming performance and exhaustive exercise in fish are often conducted on individual species, but few multispecies analyses exist and even fewer in field settings. In fish, swimming performance and exercise have historically been studied in the laboratory using swim tunnels, but an increasing body of work in recreational fisheries science provides a novel way to examine swimming capacity and exhaustion. Using fight time, the time it takes for a hooked fish to be landed on rod and reel fishing gear, as an opportunistic proxy for fish exhaustion, a multispecies meta-analysis of data from studies on recreational fisheries was conducted to elucidate the factors that most influence capacity for exhaustive exercise. Data from 39 species of freshwater and marine fish were aggregated, and negative binomial mixed effects models as well as phylogenetic least squares regression were used to identify the factors that most influenced exhaustive exercise in the field. Fish total length, aspect ratio of the caudal fin, and body form were significant factors in explaining the capacity for exhaustive exercise. Large migratory fish with high aspect ratios were able to fight, and therefore exercise, the longest. These results illustrate that body form and physiology are both deeply intertwined to inform function across fish species and point to angling fight time as a useful approximation of fish swimming capabilities that can be further developed for understanding the limits of fish exercise physiology.

AbstractReproduction represents the most energetically demanding period of life for many organisms. Capital breeders, such as anadromous sea trout (Salmo trutta), provide a particularly interesting group of organisms to study within the context of reproduction because they rely on energy stores accrued before breeding to reproduce and sustain all phenotypic and behavioral changes related to reproduction. Energy allocation into current reproduction therefore cannot be mitigated via food intake, resulting in an important life history trade-off. For this reason, exploring indexes related to energetics in salmonids can provide powerful insights into the physiological costs of reproduction. In this study, we sampled blood from and PIT tagged 232 fish captured in the wild before the spawning season. We recaptured and resampled 74 individuals (53 females and 21 males) at the end of the spawning season. Females were further divided into spawning phases (nonspawned, partially spawned, and spawned individuals), though males could not be classified as such. We compared nutritional correlates (triglycerides, cholesterol, calcium, inorganic phosphorus, and total protein), stress correlates (cortisol, sodium, potassium, chloride, and glucose), and indexes of tissue damage (aspartate aminotransferase) between initial capture and recapture as well as among spawning phases in females. We found that nutritional status decreased in all fish throughout the spawning season but that it was substantially lower in females that had spawned. We further found that spawning itself appears stressful, with elevated glucose in partially spawned females and elevated cortisol in male sea trout at recapture. Our findings thus support the idea that the cost of reproduction is energetically high and that incurred stress and a decrease in nutritional status are important physiological costs.

AbstractThis article examines hormone concentrations and body temperature (T_b) patterns of free-living thirteen-lined ground squirrels (TLGSs) across the majority of their latitudinal range in the United States (from Texas to Minnesota). Free-living TLGSs ($n=40$) were implanted with T_bdata loggers in 2019 before they entered hibernation. Three adult female TLGSs, one each from Oklahoma (low latitude), Iowa (middle latitude), and Minnesota (high latitude), were recaptured in 2020 after the hibernation season. Although this provides an n of 1 for each location and therefore no statistically supported conclusions can be drawn, the hibernation season was longest in the animal from the highest latitude with coldest winter soil temperatures (Minnesota) and shortest in the animal retrapped at the lowest latitude (Oklahoma). Torpor bouts were generally longer when soil temperatures were lower. The Iowa and Minnesota squirrels had a prolonged period of short torpor bouts with T_b near 20°C at the beginning of the hibernation season. Concentrations of the orexigenic hormone ghrelin and the sex hormones estradiol and testosterone were also compared in populations from different latitudes. In general, Minnesota males had higher testosterone than males from other populations, possibly due to a later breeding season relative to other squirrel populations. Animals trapped in early summer had significantly lower concentrations of ghrelin than those captured in midsummer, potentially driving the fat-storing period before the hibernation season. Together, these results suggest latitudinal variation in physiological regulation of circannual rhythms.

Little is known about nitrogenous waste (N waste) handling and excretion (J_{N waste}) during the complex life cycle of the sea lamprey (Petromyzon marinus), an extant jawless fish that undergoes a complete metamorphosis from a filter-feeding larva (ammocoete) into a parasitic juvenile that feeds on the blood of larger, jawed fishes. Here, we investigate the ammonia- and urea-handling profiles of sea lampreys before, during, and after metamorphosis. The rates of ammonia excretion (J_amm) and urea excretion (J_urea) significantly decreased after the onset of metamorphosis, with the lowest rates observed during midmetamorphosis. Near the completion of metamorphosis, rates of J_{N waste} ($J_{\mathrm{N waste}}=J_{a\mathrm{mm}}+J_{u\mathrm{rea}}$) significantly increased as sea lampreys entered the juvenile period. Feeding juvenile lampreys had greater than 10- to 15-fold higher J_amm and fivefold higher J_urea compared to nonfed juveniles, which corresponded to higher postprandial (postfeeding) concentrations of plasma ammonia and urea. The routes of J_amm and J_urea completely diverged following metamorphosis. In larvae, J_amm was equally split between branchial (gills) and extrabranchial (skin plus renal) pathways, but following metamorphosis, >80% of ammonia was excreted via the gills in nonfeeding juvenile lampreys, and >95% of ammonia was excreted via the gills in adult sea lampreys. Urea, on the other hand, was predominantly excreted via extrabranchial routes and, to a lesser extent, the gills in larvae and in nonfeeding juveniles. In adults, however, virtually all urea was excreted via urine. Reverse transcription polymerase chain reaction and in silico analyses also indicated that a urea transporter encoded by a slc4a2-like gene is present in lampreys. The branchial expression of this transporter is modulated throughout sea lamprey life history, as it is higher in the larvae and steadily decreases until the adult stage. We conclude that the divergent pathways of J_amm and J_urea during the sea lamprey life cycle reflect changes in their habitat, lifestyle, and diet. Further, the near-complete reliance on renal routes for J_urea in adult sea lampreys is unique among fishes and may reflect the ancestral condition of how this N waste product was handled and excreted by the earliest vertebrates.

AbstractBased on the synthesis of data on metabolic rates of 15 species investigated at moderate ambient temperatures, nestlings of most studied species of altricial rodents and lagomorphs exhibit thermoregulatory control of thermogenesis within 3 d after birth, signifying that they express physiological thermoregulation for 86%-100% of their time as nestlings. Classifying nestlings as ectotherms (or poikilotherms) is thus inappropriate and fosters misconceptions regarding their body temperatures (T_b's), control of T_b-sensitive functions (e.g., cardiac output), and energetics of development. The fact that nestlings live as litters in nests means that their thermoregulatory capacities in their actual, natural lives often far exceed the capacities they exhibit as isolated individuals-pointing to a pressing need for improved understanding of the physiology of litters. Litters in nests are already known in two cases to exhibit true homeothermy at ages when individuals studied in isolation express only modest thermoregulatory abilities. Golden (Syrian) hamster nestlings are exceptional, requiring 2 wk to develop thermoregulatory thermogenesis. They are properly considered ectotherms at up to 2 wk of age, helping to clarify that most species-being dramatically different-are not.

AbstractPigments such as melanin are most often associated with the surface of an organism, providing functions such as coloration and protection from UV radiation. However, the internal organs of some species also contain melanin. Internal melanin may also perform protective functions when cellular stress is experienced. We tested liver tissue of two tree lizard species that experienced introgression of their mitochondria to see whether melanin was present and whether it was at higher concentrations in the types of lizards thought to be under cellular stress. Previous work found that mitochondria from livers of hybrid tree lizards (those with introgressed mitochondrial DNA) had higher levels of ATP production at higher temperatures than both parental species and showed indications of dysfunction. Therefore, we predicted that if internal melanin functions to mediate the impact of damaging by-products of metabolism, such as excessive reactive oxygen species (ROS), melanin would be highest in livers of lizards with introgressed mitochondria. To test this, we used a melanin-specific stain on liver tissue sections and measured melanin concentration with spectrophotometry of heavy-membrane fractions from whole-liver homogenates of both parental species and their hybrids with introgressed mitochondria. Slides of liver sections treated with a melanin-specific stain revealed that hybrids contained melanin and had significantly higher levels of it than either parental species. Spectrophotometry gave the same result. This distribution of internal melanin matches the pattern expected if melanin functions as a compensatory mechanism to deal with higher ATP production and the subsequent high levels of ROS expected in these hybrid lizards. Future studies will examine this mechanistically.

AbstractUnderstanding the physiological adaptations of animals living in mountain landscapes is a key to predicting the responses of individuals to environmental changes, especially those imposed by climate. In this regard, the mechanism of body temperature regulation is particularly important in determining the physiological limits for activity under hypoxic and climatic stressful conditions. Numerous studies have shown that body temperature of rodents and other animals decreases with elevation and with extreme winter temperatures. But surprisingly, it is still not known how body temperature of wild animals varies along elevation during their reproductive seasons. We studied variation in core body temperature among individuals ($N=294$) of four rodent species (Apodemus flavicollis, Apodemus sylvaticus, Apodemus alpicola, Myodes glareolus) and its association with elevation (from 400 to 1,822 m asl), accounting for variation in environment temperature, microhabitat structure, body condition, and sex. Results showed a strong positive effect of elevation and a more limited effect of environmental temperature on rodents' body temperature during spring and summer. The effect of elevation on body temperature was influenced neither by interactions with environmental temperature or sex nor by the microhabitat structure. We suggest that in normothermic condition at high elevations, small mammals experiencing hypoxic exposure might show physiological adjustments for increasing efficiency of thermoregulation in low oxygen conditions.