Biology Letters最新文献

Understanding the environmental drivers of host-parasite interactions is a major concern to human health and conservation, particularly in the context of emerging infectious diseases. The likelihood of contracting an infection can be related to both the rate of contact between host and parasite, as well as innate features of hosts (susceptibility/resistance) and parasites (infectivity, virulence, within-host proliferation rate). This study uses a host-parasite system with a matching-allele model for host susceptibility and parasite infectivity to disentangle contact rate from parasite infectivity while accounting for the effects of host susceptibility. Using three exposure doses from several parasite isolates to hosts with known susceptibility, we find significant differences in parasite infectivity (in terms of number of successful infections) and within-host proliferation rate among parasite isolates, after controlling for exposure rate and host genotype. Host known susceptibility also had a strong impact on parasite infection success and proliferation rate, due to the nature of this host-parasite system. The exposure dose did not impact the number of infections or infection intensity. No significant relationship between infection success and parasite proliferation rate was detected, indicating a weak or non-existent covariance among isolates for both variables.

Due to ongoing global urbanization, some animals have settled in urban environments and rely increasingly on anthropogenic resources. One such urban adapter is the European herring gull, Larus argentatus, whose presence in towns has led to conflict with humans. Previous research has found gulls perceive men's shouting as a threat. We conducted a playback experiment on wild urban herring gulls in a foraging context to determine whether gulls perceive the difference between men shouting versus speaking the same words at the same volume, and whether those stimuli represented the same level of threat. Gulls reacted similarly to men shouting and speaking, as they flinched at the playback, exhibited vigilance, pecked less at the human food source and left the apparatus sooner than when exposed to robin song. However, gulls differentiated between the acoustic properties of men's vocalizations, as they flew away from men shouting but walked away from men speaking. When attempting to deter gulls from exploiting anthropogenic resources, talking might stop them from foraging, but shouting is more effective at making them flee.

Drive hunts in the Faroes and Japan typically involve prolonged herding of cetaceans (over hours or even days) into shallow water, forced stranding, restraint and killing using a spinal lance and exsanguination. These methods raise significant animal welfare concerns. This study applies the Five Domains Model to the Faroe Islands' grindadráp hunt to consider potential welfare implications and associated affective states. We examined published hunting guidelines and divided the hunt into six stages. Each author independently summarized potential impacts within the Five Domains Model; subsequent group consensus via online meetings assigned likely welfare impacts and affective states. Demonstrable welfare impacts and negative affective states were identified for each grindadráp stage. The prolonged chase, forced stranding, capture and restraint probably cause chronic and acute physiological stress. The spinal lance may not render animals instantaneously unconscious, raising substantial concerns that some animals may remain aware during exsanguination. Commonly inferred affective states for each domain included: pain, anxiety, disorientation, fear and panic. Given the inherent constraints of the hunt, it is unlikely that grindadráp can be undertaken humanely. If the hunt is to continue, substantial reform would be necessary to minimize animal suffering and align with welfare standards applicable to mammals in food production or research.

Sexually selected traits such as feather ornamentation of male birds can act as an impediment to movement and predator detection. Here, we report a previously undocumented example of an impediment derived from a sexually selected trait: the cranial feather ornamentation in male Chrysolophus pheasants restricting their visual field. Visual fields define the space around an animal from which visual information can be retrieved. Out of the 300 bird species studied to date, there have been no significant differences reported in the visual fields between sexes. Our findings reveal that the cranial feathers of male golden (C. pictus) and Lady Amherst's (C. amherstiae) pheasants significantly restrict their visual field relative to females and may impede their ability to gather information from the world about them. This effect is most extreme in the vertical extent, where a 30° and 40° difference is evident between the sexes of golden and Lady Amherst's pheasants, respectively. The two Chrysolophus pheasant species are the first species studied to show a difference in visual fields between sexes; this difference was absent in two closely related species also measured in this study, silver pheasants (Lophura nycthemera) and green pheasants (Phasianus versicolor).

Initiating and developing social relationships with strangers can provide fitness benefits, but it is an inherently risky process. To mitigate potential risks and develop trust, strangers may 'test the waters' by gradually escalating the type of social investment from low-cost to high-cost. Opportunities to capture the moment animals first encounter one another in the wild are rare, and detailed quantitative assessments of when and how animals initiate relationships are limited. We introduced four unfamiliar groups of feral monk parakeets together into a single 22-bird group and observed the sequence of social behaviours that occurred as relationships developed over 22 days. We tested the effect of relationship status (stranger versus familiar) on the probability of dyads following predicted sequences and whether strangers who progressed their relationships maintained higher rates of no-contact proximity compared with dyads that did not. We found that stranger dyads, but not familiar dyads, were more likely to (i) approach each other without contact before making contact and (ii) follow predicted sequences of affiliative behaviours. Strangers that progressed to contact also had higher rates of associations than did birds that never made contact. These findings provide support for 'Testing the Waters' during new relationship formation in a socially and cognitively complex species.

Human activities have disrupted the global carbon cycle, reducing carbon dioxide (CO_₂) uptake by tidal wetlands and submerged vegetation. This exacerbates climate challenges, including rising temperatures and ocean acidification. Coastal systems such as mangroves and seagrasses serve as key carbon sinks, promising for CO_₂ removal (CDR). Growing attention is being given to bivalves, whose calcification and reef-building activities shape coastal carbon dynamics. Most studies reduce bivalve impacts to a balance between individual CO_₂ emissions and the carbon stored in their shells and tissues, often overlooking species interactions-such as symbioses-that may modulate carbon fluxes. Here, we examined the mussel-symbiont holobiont using Mytilus edulis under emersion in a controlled chamber to quantify CO_₂ exchange. Mussels hosting cyanobacterial symbionts exhibited net atmospheric CO_₂ uptake during daily air exposure, a critical phase of the tidal cycle. To evaluate the potential significance at larger ecological scales, we combined laboratory-derived CO_₂ uptake data with field-based estimates of symbiont prevalence to model carbon fluxes at the mussel bed scale and compared them with values of established blue carbon systems. This research highlights the importance of species interactions in coastal carbon cycling and underscores the need to incorporate the mussel-symbiont holobiont into CDR models.

Cognitive flexibility, the capacity to adapt to changing conditions, is often assessed with reversal learning, in which a learned association must be updated after reward contingencies change. Trials-to-criterion (TTC) is a widely applied learning threshold, but it can misrepresent performance; some individuals improve steadily but fail to reach the criterion due to variability (false negatives), while others meet it through a spike without sustained learning (false positives). We evaluate TTC limitations and demonstrate learning curve analysis as a more nuanced approach to investigate learning dynamics. We tested wild striated caracaras (Phalcoboenus australis) using a two-choice discrimination task followed by a reversal task and compared TTC with trial-level modelling. Although the group showed overall improvement, individual trajectories varied widely. TTC both over- and underestimated learning, misclassifying inconsistent performers and overlooking gradual improvers. In contrast, learning curves captured trajectory, stability and consistency of change. We argue that continued reliance on binary thresholds obscures the dynamics of learning, and that slope- and trajectory-informed analyses provide a more accurate and ecologically valid framework for assessing learning in the wild.

Escape behaviours are a common response when animals encounter hypoxic environments. Confoundingly, naked mole-rats (NMRs) experience hypoxia while sleeping in crowded colony nest chambers, from which escape may not be desirable. In isolation, individual NMRs decrease physical activity to save energy in hypoxia, but this response is absent when conspecifics are present. However, whether NMRs try to escape hypoxia is unknown, as is the impact of sociality on any hypoxic escape behaviours. We predicted that individual NMRs would try to escape from hypoxic environments, but that sociality would reduce the drive to escape. We allowed individual and paired NMRs to choose between normoxia (21% O₂) or various depths of hypoxia (3%, 7% or 11% O₂) and non-invasively recorded their activity. Surprisingly, individual NMRs exhibited a novel normoxic escape behaviour and preferred severe hypoxia (3% O₂) to a normoxic environment. This preference was not repeated in less severe levels of hypoxia. Paired animals also preferred a hypoxic environment over normoxia, but social interactions drove an increase in movement velocity and reduced the severity of their preferred level of environmental hypoxia to 7% O₂. Thus, NMRs choose hypoxic environments over normoxic environments and sociality impacts this behavioural choice in hypoxia.

Distributed visual systems are composed of repeated photoreceptive units that are often assumed to be functionally and structurally identical. In chitons, shell eyes form a complex array embedded in the dorsal shell plates, with new eyes added throughout life. Using synchrotron microCT, we reconstructed all shell-eye lenses in six specimens representing five chiton species and three major lineages. We tested the relationship between lens volume and position on the shell to establish whether eyes are formed at consistent sizes. All individuals showed significant changes in eye size along the growth axis, as indicated by lens volume increasing allometrically towards the valve margins. Log-transformed mixed-effects models revealed that both lens volume and body size contribute to scaling patterns, but growth trajectories differ among species. Lens diameter can more than double from the oldest to the youngest eye, meaning individual eyes within the same individual likely have at least a fourfold difference in sensitivity. Contrary to the expectation of homogeneity in a distributed array of eyes, we show that chiton visual systems include a broad range of eye sizes within a single individual that change over ontogeny. This gradient has implications for visual functions, redundancy and the potential integration of distributed information across the shell.

Habitat adaptation critically influences relocation success in endangered reptiles. Forestland is the dominant landscape in most of the nature reserves that are used for the relocation of the Chinese alligator. To evaluate habitat suitability and utilization, we analysed movement rates and home range of Chinese alligators within a core habitat of the nature reserve, concurrently assessing habitat suitability and carrying capacity. Results indicate severely restricted annual home ranges (average 7.415 ± 7.347 × 10⁴ m² per alligator) and limited seasonal activity (March-October), with peak utilization confined to June-August in some individuals. Forestland cover significantly impeded the movement of Chinese alligators, and only 4.62% of the study area qualified as high-suitability habitat, supporting a carrying capacity of 147 individual Chinese alligators. Unsuitable habitat and climate drastically reduced the spatial and temporal utilization of the habitat. Conservation strategies should prioritize enhancing habitat quality and addressing the survival requirements and migration patterns of the Chinese alligator during the active period within nature reserves.