Biology Letters最新文献

Environmental unpredictability challenges the transmission success of vector-borne parasites like Plasmodium, whose fitness depends on synchronizing the production of transmission forms, called gametocytes, with vector availability. Although mosquito bites are known to trigger Plasmodium responses, it remains unclear whether parasites respond specifically to competent vectors or adopt a generalist strategy. We experimentally infected birds with the avian malaria parasite Plasmodium relictum and exposed them to bites from either a competent (Culex quinquefasciatus) or a non-competent (Anopheles gambiae) vector species. Both exposures induced a rise in parasitaemia, but the response was significantly stronger to the non-competent species. Host inflammatory, humoral and stress markers remained similar across mosquito treatments, implying that unidentified physiological cues may underlie the parasite's response. No species-specific modulation of gametocyte conversion rate or sex ratio was observed. These findings suggest that P. relictum does not discriminate between mosquito species, instead employing a generalist, possibly bet-hedging strategy in response to any mosquito bite. Our results highlight the importance of mosquito community composition in shaping parasite transmission dynamics. If non-vector mosquitoes enhance Plasmodium transmission investment, shifts in vector assemblages due to climate change or control measures may have unanticipated effects on disease ecology.

Many insect species are reluctant to fly freely in wind tunnels, limiting direct free-flight energetics measurements to just two species. More commonly tethered-flight energetics have been investigated, though the effects of tethering on metabolic rate are unclear. Here, we report mass-specific gross metabolic rate (assessed as the rate of carbon dioxide production; [Formula: see text]) across a speed range (0-4.1 m s^-1) in bumblebee (Bombus terrestris) workers during tethered and free flight in a closed-circuit wind tunnel. [Formula: see text] followed a U-shaped relationship with airspeed during both free (p = 0.009) and tethered flight (p < 0.001). Bees were anaesthetized with isoflurane during tethering, which had no subsequent effect on their metabolic rate (p > 0.05), avoiding issues reported during immobilization with CO₂ or cold exposure. Tethered [Formula: see text] was 45% lower than during free flight (p < 0.001), but the minimum power speed and the trajectory of the metabolic power-speed relationship (p > 0.8) were similar. Overall flight efficiency ranged from 7.3 to 14.7% and did not vary with airspeed. These findings confirm a U-shaped metabolic power-speed relationship in insects, and suggest that tethered flight may approximate free-flight energetics. However, a shift in the maximum range speed to slower speeds during tethered flight warrants caution against using this variable to predict behaviour.

Social rewards may have evolved in social species to reinforce adaptive social interactions. Yet, evidence for social rewards is still scarce, and the underlying mechanisms remain unclear. A key candidate to regulate the value of social stimuli is oxytocin due to its role in social affiliation, which is traced to its origins in ray-finned fish-but whether it encodes rewards is uncertain. Using a single-trial conditioned place preference test, we found that wild-type zebrafish increased preference for a neutral unpreferred cue associated with a same-sex sibling, while oxytocin receptor (oxtr) mutants did not. These findings demonstrate the necessity of oxtr for social rewards, while the short exposure infers its role in encoding rather than consolidation. Our results provide evidence for an evolutionarily conserved role of oxytocin in social reward encoding given the available evidence for similar effects in rodents.

Despite increased recent attention towards Bayesian phylogenetics and its applications in understanding macroevolutionary processes, it remains unclear how many discrete characters are needed to accurately estimate tree topologies in a Bayesian framework. This could be particularly relevant for morphological datasets used in phylogenetics, as they usually consist of few dozens to few hundreds of characters-orders of magnitude smaller than most molecular datasets. I designed a simulation study in the software RevBayes to explore how the number of sampled discrete characters affects accuracy and precision of Bayesian phylogenetic estimates, under various set-ups differing in number of taxa, average number of state changes per character (i.e. tree length) and number of states per character. Results indicate that between 100 and 500 variable characters are necessary to reach sufficient accuracy and precision of phylogenetic estimates for as low as 20 tips. All other parameters being equal, multistate characters produce slightly more accurate estimates than binary characters and more labile characters produce more accurate estimates for trees above 50 tips. The results of this study highlight the continuous need for global research efforts geared towards the characterization and digitization of interspecific morphological diversity in both extant and extinct taxa.

Diagnostic ultrasound imaging is vital in human and veterinary medicine, facilitating non-invasive examinations and enhancing clinical outcomes. However, despite the increasing advances in ultrasound technology, there are few animal studies comparing scanner performance, particularly between cart-based and handheld models. We evaluated the performance of three ultrasound scanners-the cart-based Sonosite Edge II and handhelds Clarius Scanner C3 HD3 and Edge SS-H6-on mammary gland assessment of female Atlantic bottlenose dolphins (Tursiops truncatus) under human care. Advantages and disadvantages of each scanner for field-based measurements were assessed. Sonosite provided superior image quality but was unsuitable for performing scans in sea pens due to its weight, need of AC power and lack of waterproofing. Clarius and Edge offered greater portability, allowing examinations during adverse weather, although Wi-Fi connectivity could be hampered if mobile devices linked to the transducer connected to other networks during scanning. In showing that mammary glands increase in thickness with age, we highlight the need for consistent equipment use for organ measurements, as the variability among scanners could impact assessments and physiological interpretations (e.g. reproductive stage). This research emphasizes the importance of environmental factors and device characteristics when selecting ultrasound equipment for marine mammal studies in artificial and natural habitats.

The magnetic sense remains one of the mysteries of sensory biology. Despite 50 years of extensive research, science seems to be at a standstill. One of the major factors contributing to this scientific stasis is the lack of simple, reproducible model systems. Here, we examine magnetoreception in earthworms held in transparent soil. Using video recordings and machine learning-based analysis, we show that earthworms move significantly less when held in a near-zero magnetic field (nZMF). This effect of nZMF on earthworm activity was highly reproducible and significant through all trials. Furthermore, under some circumstances the earthworms showed significant group magnetic directionality; however, this result was not reproducible. By using earthworms in transparent soil and manipulating the magnetic field, we created a robust protocol that facilitates examination of magnetoreception in a simple organism. This may serve as a crucial springboard in the ongoing quest to unravel this mysterious sense.

Formally describing cryptic species is essential for conservation and protection purposes and to enable their use in environmental monitoring. The current scientific practice in many invertebrate groups requires assigning the original morphospecies name to a particular genetic lineage before formally describing the other lineages of the morphospecies and providing an exhaustive morphological characterization for each described lineage of the morphospecies. These practices considerably delay-and may even hinder-the scientific description of cryptic species. Furthermore, it may lead to confusion if the same name refers to both the entire morphospecies and a particular lineage. Here, we propose some recommendations to accelerate the description of cryptic species and avoid taxonomic confusion. They include assigning a new name to each lineage of the morphospecies without (necessarily) first obtaining DNA from the morphospecies holotype or paratype(s) or designating a neotype, providing a basic morphological diagnosis in the cryptic species descriptions, and systematically following the morphospecies names by 'sensu lato' or 'species group' when referring to the entire morphospecies and by 'sensu stricto' when referring to the original lineage. Our recommendations could contribute to rapidly increasing the proportion of scientifically described cryptic species and enhancing the consideration of cryptic species in ecological assessments and conservation/protection programmes.

Antarctic krill (Euphausia superba) are a key species in the marine Antarctic ecosystem. Food boluses, a by-product of feeding where Antarctic krill form a compact food mass within their feeding basket, were formed and rejected under laboratory conditions. We explored the conditions leading to bolus formation by examining feeding behaviour of Antarctic krill in response to different phytoplankton types and concentrations. Two scenarios were observed that increased the likelihood of bolus formation: (i) when food concentrations exceed the krill's filtering capacity and (ii) when particles are caught in the feeding basket. We measured the frequency of rejection of boluses, along with their composition, carbon and nitrogen contents, and sinking rates. For cell concentrations approximately 10⁸ cells l^-1, the frequency of rejection ranged from 2.6 to 17.0 boluses per hour. The carbon and nitrogen contents averaged 24.1 µg C mm^-3 and 2.3 µg N mm^-3, and sinking rates averaged 367 m d^-1. Our findings suggest this behaviour may also occur in situ and could contribute to organic carbon export, with bolus sinking rates comparable to or exceeding those of Antarctic krill faecal pellets. If confirmed in the field, this behaviour may also occur in other krill species with similar feeding behaviours.

Pigmentation in mammalian hair follicles is governed in part by interactions between agouti signalling protein (ASIP) and the melanocortin 1 receptor (MC1R). The most common coat colours in mammals result from alternating bands of dark eumelanin and light phaeomelanin within individual hair shafts. However, coats dominated by a single melanin have arisen several times. Here, we examine the genetic basis of two instances in marsupials: a melanistic morph of the eastern quoll (Dasyurus viverrinus) found at high frequency in the wild, and a rare case of fixed xanthism in the marsupial moles. In eastern quolls, we identify a deletion encompassing the ASIP start codon which was found to be homozygous only in the melanistic animals examined. This mutation appears to be convergent with that recently discovered in its dark-coated relative, the Tasmanian devil (Sarcophilus harrisii). Conversely, we show that a non-sense mutation which severely truncates MC1R in the southern marsupial mole (Notoryctes typhlops) is a candidate driver of its pale-yellow coat. Together with other recent findings, our results suggest that loss-of-function mutations have occurred repeatedly within the marsupials, representing a mechanism underpinning coat colour variation.

The 'Chicago Rat Hole' is a remarkable full body impression ostensibly created by a brown rat (Rattus norvegicus) crossing fresh concrete in Chicago's Roscoe Village that became a viral sensation. While the public attributed the mark to a brown rat, no formal analysis had been conducted to confirm its identity. Using clear anatomical landmarks, we compared measurements from the 'Chicago Rat Hole' to eight sympatric rodent species using univariate and multivariate analyses. Univariate tests showed no significant differences in snout-to-tail length, head width, tail-base width or third digit length between the imprint and members of the genus Sciurus (i.e. tree squirrels). Discriminant function analysis indicated a 98.67% likelihood that the 'Chicago Rat Hole' was a squirrel, with classifications split between the eastern grey squirrel (50.67%) and the fox squirrel (48.00%). Given local population densities, an eastern grey squirrel likely represents the most parsimonious species-level match. This investigation underscores the challenges of attributing a trace to the tracemaker. While we acknowledge the playful spirit of this investigation, our broader aim is to highlight that scientific inquiry begins with curiosity and observation: qualities that are not exclusive to professional scientists, but accessible to anyone with an interest in understanding the natural world.