Biology Letters最新文献

A distinct shoulder region, defined by endoskeletal and dermal girdles and associated pectoral musculature, is a major evolutionary adaptation of jawed vertebrates. In teleost model species, the large (macromeric) pectoral dermal bones can be derived from multiple embryonic tissues, identifying the shoulder of osteichthyans as a developmentally complex area at the head-trunk boundary. The absence of bone in living chondrichthyans makes Palaeozoic stem groups capable of dermal ossification key to understanding the underpinnings of skeletal growth in the shoulder of crown gnathostomes (osteichthyans and chondrichthyans). Here, using synchrotron X-ray tomography we demonstrate that individual pectoral plates in the oldest unequivocal jawed vertebrate, the Silurian (c. 439 Mya) chondrichthyan Fanjingshania renovata, develop from five separate growth centres. These centres correspond to pectoral bony spines that fuse neighbouring dermal scales into a pinnal plate and their expansion is accompanied by cyclical resorption and remodelling of bone and dentine. Our phylogenetic analyses support an interpretation of these processes as crown and stem gnathostome characters that co-occur only in the shoulder girdle of stem chondrichthyans. The systematic hard tissue remodelling in Fanjingshania reveals an unexpected growth dynamic within chondrichthyans that relates to the formation of a macromeric skeleton through integration of modular elements.

Neuroplasticity enables the brain to adapt neural activity, but whether this can be harnessed for abstract optimization tasks like seeking curve extrema remains unclear. Here, we used a brain-machine interface in mice, pairing auditory feedback of neuronal firing rate with water rewards, to investigate whether motor cortex neurons can optimize activity along a unimodal curve ([Formula: see text]). The curve maps firing rate ([Formula: see text]) to sound frequency increase speed ([Formula: see text]), where the curve extremum accelerates reward acquisition. Over conditioning sessions, mice learned to modulate firing rates towards this peak, reducing reward time from 18.64 ± 7.30 s to 11.59 ± 4.38 s and increasing high-response events from 66 to 104 occurrences. Putative neurons increasingly prioritized high-response intervals, with positive proportion increments in upper intervals versus negative trends in lower ones. These findings demonstrate that cortical neurons can dynamically optimize activity along non-monotonic reward landscapes, revealing neuroplasticity as a substrate for adaptive self-optimization. This expands our understanding of how the brain learns abstract rules via feedback, with implications for neuroprosthetic design that leverage neural adaptability.

Testing if non-human taxa experience pain is difficult because we need to exclude the possibility that responses are nociceptive reflexes. One approach is to identify an essential, high priority, resource and then ask if the animal will abandon and subsequently avoid that resource if it is paired with a noxious stimulus. This approach has been used with crustaceans that hide in dark shelters and electric shocks have been used as noxious stimuli. A range of species show escape responses and avoid shelters if the shock is presented within, and these responses increase with increasing voltage or repetition of shocks. Crustaceans also switch to using alternative shelters and appear to dramatically alter their behavioural priorities. Animals shocked outside of a shelter, however, subsequently increase their use of shelters and benefit from reduced predation. These changes in priorities cannot be due only to nociceptive reflexes because they persist long after the cessation of the stimulus. Increasing the apparent costs of leaving a shelter decreases the probability of leaving, indicating that, by taking into account costs, they are responding via behavioural decisions and not reflexes. This provides a method to determine how much the animal will pay to avoid the shocks and similar techniques should provide powerful ways to examine potential pain in different taxa.

Arboreal locomotion presents considerable mechanical challenges, requiring animals to maintain stability on narrow supports. While some species rely on gait adjustments, others use grasping autopodia to counteract toppling torques. We investigated how substrate size affects grasping force in strepsirrhine primates-a lineage regarded as a model for early primates and known for fine-branch arboreal locomotion. Using a custom apparatus, we measured in vivo grip strength across three substrate diameters (small, medium and large) in 11 species. In both hands and feet, grip strength peaked on medium-sized substrates-those allowing optimal digital wrapping-and declined on small and large diameters. These patterns remained significant after controlling for phylogeny, body size, sex and age. Despite weaker performance on small substrates, strepsirrhines commonly navigate thin terminal branches in nature, suggesting an ecological mismatch between peak grasping performance and substrate use. This implies that powerful digital grasping may be less critical for arboreal stability than often assumed. Instead, whole-body mechanics and precise limb placement likely compensate when grip is reduced. Rather than maximizing force, the primate hand appears adapted for versatility-supporting the broader principle that evolutionary success often reflects functional adequacy and adaptability over specialization for force production.

Accurately identifying evolutionarily significant units (ESUs) is crucial for conservation planning, especially for species like pangolins threatened by overhunting and habitat loss. ESUs help categorize different pangolin populations, aiding in understanding their genetic diversity and distribution, which is vital for targeted conservation efforts. This research generated mitochondrial genomes from historical museum specimens of Sunda pangolins (Manis javanica) from underrepresented locations, uncovering a new evolutionary lineage from the Mentawai Islands that diverged from Indochina and west Sundaland populations around 760 000 years ago. This population thereby represents a divergent ESU with a small distribution, important for conservation planning. The novel sequences provide resources for forensic labs tracing the origin of confiscated scales and shed light into the potential distribution of the 'mysterious pangolin'. Additionally, this research confirmed the presence of the two major M. javanica lineages in Java and extended the known distribution of the eastern clade to Bali and East Kalimantan. Our findings potentially suggest a recent bottleneck and postglacial expansion of pangolins across Indochina and west Sundaland. Further investigation with genomic and morphological evidence, contact area sampling and type sequencing will be required to evaluate the taxonomic status of different M. javanica lineages and M. culionensis.

Body length is a crucial ecological predictor in vertebrates, yet total body length proxies have seldom been assessed for ancient marine top predators. Here, we test the strength of phylogenetic imputation and 23 linear measurements, sampling both broad skeletal regions and frequently fossilized elements (such as vertebral centra), in predicting the body length of the main clades of tail-propelled Mesozoic marine reptiles (Ichthyosauria, Mosasauridae and pelagic thalattosuchians). We embed this marine reptile sample within a comparative framework with raptorial cetaceans, and analyse the evolution of body proportions in these clades. We find that trunk length and centrum dimensions are strong predictors of body length, opening up the possibility to build vast datasets of body length estimations for Mesozoic marine reptiles from minimal preserved remains. We provide body length calculation equations for all traits and all clades. Proxies fared much better and often had distinct slopes when applied clade-wide rather than when applied to the global dataset. We also show that body length in Mesozoic marine reptiles is more labile than their skeletal architectures, rendering phylogenetic imputation methods less effective than skeletal proxies for assessing body lengths.

Passive acoustic monitoring is an observation method for detecting and characterizing ocean soundscapes, and it has recently been used to observe underwater marine life. The brown croaker (Miichthys miiuy) is an important fish species in the Northwest Pacific Ocean that produces biological sounds. In this study, the sounds of 150 adult brown croakers were recorded continuously for three weeks using a self-recording hydrophone. The acoustic parameters of their calls, choruses and vocalization patterns were analysed using environmental factors from the ocean. The brown croaker's call sound with zero peak sound pressure level was 150.8 dB, but the chorus sound was relatively high at 161.3 dB. The vocalization of the sounds occurred daily around sunset and dusk and was associated with decreased spawning activity when the water temperature decreased below approximately 25°C. The acoustic characteristics of the brown croaker's sounds will help improve ocean soundscape management to protect the marine ecosystem and identify spawning and fishing grounds.

'Thecodont' refers to teeth implanted in sockets within the jaw, a condition traditionally associated with living mammals and crocodylians, which also coincidentally have teeth attached by ligaments to the socket walls (gomphosis). For over a century, the bony periodontium of many other amniotes has been described as a single tissue, 'bone of attachment', causing confusion over dental tissue homology. The conventional definitions of 'thecodonty' exclude species with fused teeth ('ankylothecodonts'), implying a fundamental difference between mammals, crocodylians and most other vertebrates. However, the stereotypically 'thecodont' attachment tissues have been discovered in representatives of all major amniote clades, showing that gomphosis and ankylosis likely stem from heterochronic changes in the timing and extent of cementum and alveolar bone mineralization. This challenges (i) previous hypotheses regarding the evolution of the amniote periodontium, (ii) the 'bone of attachment' paradigm, and (iii) the significance of 'thecodonty'. We suggest a new nomenclatural approach that incorporates recent histological and evolutionary research and divides thecodonty into anatomical categories to clarify their origin and evolution. We propose the terms anisothecodont and isothecodont to denote, respectively, asymmetric and symmetric implantation of teeth in their sockets. Regardless of the geometry of the connection, we propose using ankylosis and gomphosis to denote the mode of tooth attachment.

Theoretical and empirical considerations suggest that relatedness can have complex effects on social life. While high relatedness may promote sibling cooperation and altruism through indirect fitness benefits, it can also intensify competition if siblings share similar needs and competitive strategies. Moreover, low genetic diversity in highly related groups may heighten susceptibility to pathogens. Hence, due to these potential opposing effects, the consequences of relatedness for offspring fitness within a family context are not fully understood. Here, we investigated how relatedness among interacting offspring influences their fitness in the burying beetle Nicrophorus vespilloides, a species exhibiting facultative parental care, with larvae developing in a microbially rich and challenging environment. To assess offspring effects without parental influence, we raised larvae in the absence of care, thereby eliminating parental buffering and exposing them to a more stressful environment. We compared the growth and survival rates of broods consisting of full siblings and broods with unrelated larvae and found both benefits and costs of relatedness. Larvae gained weight more rapidly in the early stages when surrounded by siblings but suffered higher mortality later in development. These findings suggest that high relatedness facilitates cooperative effects but comes at a cost, potentially reducing social immunocompetence.

Animal genitalia typically exhibit limited size variation relative to overall body size, a pattern known as negative allometry. The 'one-size-fits-all' hypothesis suggests that genital compatibility between sexes constrains the evolution of extreme genital sizes, yet direct evidence remains scarce. Drosophila suzukii presents a unique opportunity to test this hypothesis from the female perspective. This species has evolved an enlarged, sclerotized ovipositor capable of piercing intact fruit skins. However, this innovation necessitated an altered genital coupling mechanism, as the modified ovipositor-also functioning as part of the female genitalia-posed a mechanical obstacle to copulation. In contrast, D. subpulchrella, the closest relative of D. suzukii, retains the ancestral coupling mechanism, which depends on genital size compatibility between sexes. Allometric analyses revealed that D. subpulchrella ovipositors exhibit shallower scaling slopes than other body parts, consistent with the negative allometry rule. Conversely, D. suzukii ovipositors display significantly steeper slopes, suggesting that the new coupling mechanism has relaxed the constraint on genital size. These findings provide novel support for the one-size-fits-all hypothesis, offering unprecedented resolution into the role of coupling mechanisms in shaping genital allometry.