Despite growing interest in animal social networks, surprisingly little is known about whether individuals are consistent in their social network characteristics. Networks are rarely repeatedly sampled; yet an assumption of individual consistency in social behaviour is often made when drawing conclusions about the consequences of social processes and structure. A characterization of such social phenotypes is therefore vital to understanding the significance of social network structure for individual fitness outcomes, and for understanding the evolution and ecology of individual variation in social behaviour more broadly. Here, we measured foraging associations over three winters in a large PIT-tagged population of great tits, and used a range of social network metrics to quantify individual variation in social behaviour. We then examined repeatability in social behaviour over both short (week to week) and long (year to year) timescales, and investigated variation in repeatability across age and sex classes. Social behaviours were significantly repeatable across all timescales, with the highest repeatability observed in group size choice and unweighted degree, a measure of gregariousness. By conducting randomizations to control for the spatial and temporal distribution of individuals, we further show that differences in social phenotypes were not solely explained by within-population variation in local densities, but also reflected fine-scale variation in social decision making. Our results provide rare evidence of stable social phenotypes in a wild population of animals. Such stable social phenotypes can be targets of selection and may have important fitness consequences, both for individuals and for their social-foraging associates.

Summary Forelimb navicular bones and associated soft tissues were collected from 3 groups of horses and subjected to pathological examinations. The groups consisted of 38 horses with clinical navicular disease (ND) and 2 control groups, with no history of forelimb lameness, consisting of 25 age‐matched mature horses (A‐MC) and 9 immature horses (IC). Histological and histomorphometric studies were performed on tissue samples from 10 ND, 10 A‐MC and 5 IC horses. Gross changes seen only in ND horses included: full thickness defects in the palmar surface fibrocartilage, palmar cortex erosion, medullary lysis, flexor digitorum profundus tendon (FDPT) surface fibrillation, FDPT core lesions and adhesions between the FDPT and navicular bone. Palmar surface partial thickness fibrocartilage loss and distal border fragmentation were seen with a significantly greater incidence in ND than in A‐MC and not observed in IC. Remodelling of the proximal border, FDPT surface colouration, palmar surface fibrocartilage colouration and proximal border entheseous bone were identified in ND and A‐MC but not in IC. Mid‐ridge synovial fossae and horizontal depressions in the palmar surface were identified in all groups. Histologically palmar fibrocartilage thinning and loss were associated with reduced palmar fibrocartilage cell density and chondrocyte cluster formation. Palmar fibrocartilage fibrillation, palmar cortical bone defects, fibromyxoid stromal change in the medulla, medullary pseudocyst formation and entheseous new bone formation were all seen in ND. The adjacent FDPT showed fibrillation, tag formation and degeneration of the dorsal surface. Necrotic foci were also present within the body of the tendon. Although not always present, medullary bone pseudocysts, separate mineralised foci and most changes on the dorsal surface of the FDPT were specific to ND. Bone histomorphometric parameters were compared among groups. Cross‐sectional area reduced from the sagittal ridge to the medial and lateral margins of each navicular bone. IC navicular bones had a smaller subchondral area, subchondral bone volume and a greater osteoid volume than in the AC, indicating that these differences were age‐related. In ND the medullary area was decreased but the trabecular bone volume increased. The palmar subchondral area was increased but contained bone with an increased porosity and osteoid volume. Changes occurred from the medial to the lateral margins of the bone in horses with ND indicating remodelling of the bony elements throughout the bone in ND. The histological and histomorphometric changes in the navicular bone and palmar fibrocartilage were considered similar of those found in articular hyaline cartilage and subchondral bone in osteoarthritis.

Loading of the rat ulna is an ideal model to examine stress fracture healing. The aim of this study was to undertake a detailed examination of the histology, histomorphometry and gene expression of the healing and remodelling process initiated by fatigue loading of the rat ulna. Ulnae were harvested 1, 2, 4, 6, 8, and 10 weeks following creation of a stress fracture. Stress fracture healing involved direct remodelling that progressed along the fracture line as well as woven bone proliferation at the site of the fracture. Histomorphometry demonstrated rapid progression of basic multicellular units from 1 to 4 weeks with significant slowing down of healing by 10 weeks after loading. Quantitative PCR was performed at 4 hours, 24 hours, 4 days, 7 days, and 14 days after loading. Gene expression was compared to an unloaded control group. At 4 hours after fracture, there was a marked 220-fold increase (P<0.0001) in expression of IL-6. There were also prominent peak increases in mRNA expression for OPG, COX-2, and VEGF (all P<0.0001). At 24 hours, there was a peak increase in mRNA expression for IL-11 (73-fold increase, P<0.0001). At 4 days, there was a significant increase in mRNA expression for Bcl-2, COX-1, IGF-1, OPN, and SDF-1. At 7 days, there was significantly increased mRNA expression of RANKL and OPN. Prominent, upregulation of COX-2, VEGF, OPG, SDF-1, BMP-2, and SOST prior to peak expression of RANKL indicates the importance of these factors in mediating directed remodelling of the fracture line. Dramatic, early upregulation of IL-6 and IL-11 demonstrate their central role in initiating signalling events for remodelling and stress fracture healing.

Summary Analgesia of the distal interphalangeal (DIP) joint and of the navicular bursa was performed independently in the lame or lamer forelimb of 59 horses, in which lameness was significantly improved by perineural analgesia of either the palmar digital or palmar (abaxial sesamoid) nerves. In 3 horses no improvement was detected. Lameness was improved by analgesia of the DIP joint but there was no response to analgesia of the navicular bursa in 3 horses. In 12 horses, lameness was improved by analgesia of the navicular bursa but intra‐articular analgesia resulted in no change. Forty‐one horses responded both to analgesia of the navicular bursa and intra‐articular analgesia of the DIP joint. Synovial fluid was retrieved from all DIP joints but from only one navicular bursa. It is suggested that a positive response to analgesia of the DIP joint does not necessarily imply that pain arises from the joint per se, but a positive response to intra‐bursal analgesia probably reflects pathology of the bursa per se, the navicular bone and/or supporting ligaments and/or the DDFT. Radiographic abnormalities of the navicular bone in the lame or lamer limb were detected in 35 horses, all of which showed some response to analgesia of the navicular bursa. In 25 of these horses (71%) changes were only identifiable in the palmaroproximal‐palmarodistal oblique views. There was a higher incidence of radiographic abnormalities of the navicular bone in horses in which the response to intraarticular analgesia of the DIP joint was similar (70%) to, or greater (71%) than analgesia of the navicular bursa, compared with the groups in which there was no response (58%) or a lesser response (62%) to intra‐articular analgesia. The front feet of 6 horses were examined post mortem. All horses had pathological abnormalities of the flexor surface of the navicular bone of the lame or lamer limb and in 5 there was associated fibre damage of the opposing deep digital flexor tendon. No abnormalities of the DIP joint were identified. We suggest that, when possible, if foot pain is suspected, the following analgesic techniques should be performed in sequence, but on different occasions: (1) perineural analgesia of the palmar digital (and when necessary palmar [abaxial sesamoid]) nerves; (2) analgesia of the DIP joint; and (3) analgesia of the navicular bursa.

Both social and ecological factors influence population process and structure, with resultant consequences for phenotypic selection on individuals. Understanding the scale and relative contribution of these two factors is thus a central aim in evolutionary ecology. In this study, we develop a framework using null models to identify the social and spatial patterns that contribute to phenotypic structure in a wild population of songbirds. We used automated technologies to track 1053 individuals that formed 73 737 groups from which we inferred a social network. Our framework identified that both social and spatial drivers contributed to assortment in the network. In particular, groups had a more even sex ratio than expected and exhibited a consistent age structure that suggested local association preferences, such as preferential attachment or avoidance. By contrast, recent immigrants were spatially partitioned from locally born individuals, suggesting differential dispersal strategies by phenotype. Our results highlight how different scales of social decision-making, ranging from post-natal dispersal settlement to fission–fusion dynamics, can interact to drive phenotypic structure in animal populations.

Social network analysis has become a popular tool for characterising the social structure of populations. Animal social networks can be built either by observing individuals and defining links based on the occurrence of specific types of social interactions, or by linking individuals based on observations of physical proximity or group membership, given a certain behavioural activity. The latter approaches of discovering network structure require splitting the temporal observation stream into discrete events given an appropriate time resolution parameter. This process poses several non-trivial problems which have not received adequate attention so far. Here, using data from a study of passive integrated transponder (PIT)-tagged great tits Parus major, we discuss these problems, demonstrate how the choice of the extraction method and the temporal resolution parameter influence the appearance and properties of the retrieved network and suggest a modus operandi that minimises observer bias due to arbitrary parameter choice. Our results have important implications for all studies of social networks where associations are based on spatio-temporal proximity, and more generally for all studies where we seek to uncover the relationships amongst a population of individuals that are observed through a temporal data stream of appearance records.

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