A breeding programme to develop a line of chickens with a high incidence of tibial dyschondroplasia (TD) from Australian broiler stock is described. Despite the absence of a control flock, this programme has demonstrated that selection in a broiler population can rapidly increase the incidence of TD. There was consistent circumstantial evidence of the presence of a major sex-linked gene, the recessive allele of which is associated with an increased incidence of TD. The realised heritability estimates (obtained in the absence of a control flock) consistently exceeded 1.00, suggesting the presence of an environmental trend favourable to the onset of TD over the four generations of this investigation. There was a high maternal component or dominance genetic component, or both, for the inheritance of TD in the final generation, suggesting that environmental factors associated with the female parent line may influence the incidence of TD in broilers.

1. To survey the relationship between tibial dyschondroplasia (TD) and the down-grading of broiler carcasses three processing plants representing the major breeding and growing organizations in Australia were visited. 2. The incidence of TD for the three flocks examined varied from 14 to 35%. In the flock with the highest incidence of TD there was a direct relationship between the presence of TD and down-grading of carcasses due to leg abnormalities. 3. A genetic analysis was carried out on one of the parent lines of the breeding group with the highest TD incidence. The genetic correlation between body weight and TD incidence at 7 weeks of age was negative, suggesting that continued selection for increased body weight should lead to a reduced incidence of TD. Since this conflicts with usual expectations, possible reasons, including a within-line genotype by environment interaction, are discussed. 4. Because of the substantial genetic component associated with TD, screening of breeding cockerels for its presence if strongly recommended.

Patterns of colonisation and breeding behaviour were observed in part of the Grey seal rookery at North Rona during the entire breeding season in 1972. Bulls came ashore when pupping started and joined cows grouped around pools. Numbers of cows and bulls increased to maxima in three and five weeks respectively. Limited access to the rookery and the presence of pools and waterlogged ground influenced site selection by cows. In the study area the breeding season lasted for 74 days, with individual bulls staying for periods varying from 6–57 days. Daily ratios of bulls to cows varied, but the average ratio was 1:7‐5. It was estimated that 275 cows participated in mating, compared with 37 bulls, during the entire breeding season. The interval of 18 days between peak numbers of cows and bulls ashore corresponded closely with the average time that cows spent ashore. The aggressive responses of cows in mating behaviour were noted during observations of 114 copulations. It was concluded that a bull requires a very strong sexual drive in order to overcome a cow's aggressive responses, and this reinforces the selective advantage of aggressive dominance in bulls. The stimulus inducing a bull to attempt mating seemed to be the presence of oestrous cows in the rookery rather than an individual cow being in oestrus, because the number of attempted copulations increased even when the number of cows in oestrus temporarily declined during the season. Direct observations and calculations using an index of copulation suggested that the copulation frequency for individual cows ranged from 2.5‐3.6. A bull's participation in mating, and therefore, its genetic influence, was related to the length of its stay in the rookery, and from this evidence it was deduced that a social hierarchy existed amongst the bulls. Appraisal of the results led to the conclusion that the Grey seal bull maintains a high level of sexual activity so as to mate with as many cows as possible, rather than ensuring exclusive access to cows through territorial fighting and boundary display.

The Grey seal breeding assembly on North Rona was studied throughout autumn 1972. Weekly censuses provided data on birth rate and mortality. It is estimated that 1736 pups were born in 1972. This is about 500 less than the mean production estimate for this assembly during the period 1959–71, possibly a result of disturbance of the breeding site by the expedition. About 600 of the pups died before putting to sea. The mean date of birth and the duration of the pupping season agree closely with earlier work on North Rona, although the mean daily birth rate curve is somewhat irregular, perhaps because there was an unusually dry spell of weather at a critical time in the pupping season. An improved estimate of mortality at this assembly showed a relationship with pup density similar to that observed at the Fame Islands. Techniques for estimating pup production (and consequently total population), though not reliable for determining absolute values, are useful for indicating trends and they suggest a stable population of 8000–9000 animals at North Rona. Such estimates might be improved by the use of better methods of aerial photography.

Births and postnatal behaviour were observed at a breeding assembly of Grey seals on North Rona. Birth is extremely rapid and the cow immediately turns to smell the pup. Smelling continues at intervals, particularly during the first 10 min after birth and allows the cow to establish the identity of her pup. She also smells the placenta and defends it against attack by gulls. Disturbance by gulls, neighbouring seals and human intrusion may lead to the cow failing to establish a bond with the pup and consequently abandoning it.

No abstract

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31In response to rapid environmental change, organisms rely on both genetic 32 adaptation and phenotypic plasticity to adjust key traits that are necessary for survival and 33 reproduction. Given the accelerating rate of climate change, plasticity may be particularly 34 important. For organisms in warming aquatic habitats, upper thermal tolerance is likely to 35 be a key trait, and many organisms express plasticity in this trait in response to 36 developmental or adulthood temperatures. Although plasticity at one life stage may 37 influence plasticity at another life stage, relatively little is known about these interactive 38 effects for thermal tolerance. Here we used locally adapted populations of the intertidal 39 copepod Tigriopus californicus to investigate these interactions in a marine ectotherm. 40We found that low latitude populations had greater critical thermal maxima (CT max ) than 41 high latitude populations, and variation in developmental temperature altered CT max 42 plasticity in adulthood. After development at 25°C, CT max was plastic in adults, whereas 43 no adult plasticity in this trait was observed after 20°C development. This pattern was 44 identical across four populations, suggesting that local thermal adaptation has not shaped 45 this interactive effect. However, differences in the capacities to maintain ATP synthesis 46 rates and to induce heat shock proteins at high temperatures, two likely mechanisms of 47 local adaptation in this species, were consistent with changes in CT max due to 48 developmental temperatures, suggesting there is mechanistic overlap between plastic 49 interactions and adaptation in general. These results indicate that interactive effects of 50 plasticity across life stages may have substantial impacts on upper thermal tolerance in 51 ectothermic organisms.