Environmental Influence on Life-History Traits in Male Squid Uroteuthis Edulis With Alternative Reproductive Tactics

Squid are characterized by flexible life-history traits (LHTs) that change in response to changing oceanic parameters. Male alternative reproductive tactics (ARTs), characterized by large-sized ‘consorts’ versus small-sized ‘sneakers’, are commonly observed in loliginid species. This study reports on LHTs flexibility in male squids displaying ARTs. LHTs of consorts and sneakers in Uroteuthis edulis, including body size, age, growth rate and gonado-somatic energy allocation, were compared among seasonal and geographical groups from Japan and Taiwan. The ratio of consorts to sneakers was highest in the group spawning in the ‘Japan-warm’ season (June-November), followed by that of the ‘Japan-cold’ season (December-May), and lowest in Taiwan (spring and autumn). LHTs were compared among cohorts separated by hatching season and catch location (Jwarm, Jcold and Taiwan cohorts). Mean body size of consorts showed no difference among cohorts, although Taiwan consorts were relatively younger than Japan consorts. Mean size and age of sneakers decreased with increased water temperature at hatching. Growth rates of consorts and sneakers were slightly different among cohorts, in accordance with differences of statolith increment widths during their early life stage (50-150 d). Growth rates of both consorts and sneakers were highest in the Taiwan cohort, followed by the Jwarm cohort, with the Jcold cohort lowest. Sneakers invested more both in mantle and gonadal weights than consorts in all cohorts. Gonado-somatic energy allocation patterns of consorts and sneakers were consistent at different temperatures. LHTs of U. edulis consorts and sneakers were strongly influenced by temperature, with higher flexibility in sneakers than consorts.

Life history contrasts in nutritional state and return probability of post-spawned Atlantic salmon

Using non-lethal tissue biopsies, we investigated somatic energy, lipid composition, and condition in post-spawned Atlantic salmon (kelts, n = 69) returning to sea in the spring and explored contrasts as a function of previous migration- and spawning history, length and sex. Using mark-recapture analysis, we also explored linkages between spawning history and probability of future repeat spawning. Lipid density was significantly higher in previously spawned individuals compared to first time spawned fish, and in females compared to males. Fatty acid composition differed significantly among spawning histories. Return rates to consecutive spawning the following year were consistent with spawning history dependent differences in lipid density, as first time spawned kelts had lower return rates compared to consecutive repeat spawned kelts. We suggest that spawning history related contrasts in nutritional state in post-spawned Atlantic salmon may be a carry-over effect of differences in the feeding habitat as affected by spawning-history dependent migration strategies. Alternatively, it may represent an adaptive response to increased survival and recovery potential with age.

Lead pollution and the Roman economy

More than a decade ago, the Oxford Roman Economy Project (OXREP)1 and the Cambridge economic history of the Greco-Roman world put the question of the performance of the Roman economy at the center of historical debate, prompting a flood of books and articles attempting to assess the degree of growth in the economy.2 The issue is of sufficient importance that it has figured in the narratives of economists analyzing the impact of institutional frameworks on the potential for growth.3 As the debate has continued, there has been some convergence: most historians would agree that there was some Smithian growth as evidenced by urbanization and trade, while acknowledging that production remained predominantly agricultural and based primarily on somatic energy (i.e., human and animal).4 This is, of course, a very broad framework that does not differentiate the Roman empire from other complex pre-industrial societies. The challenge is to refine the analysis in order to put content into the broad description of “modest though significant growth”5 and to offer a deeper understanding of the dynamics of the economy.

Exposure to high temperature influences the behaviour, physiology, and survival of sockeye salmon during spawning migration

Since 1996, some populations of Fraser River sockeye salmon ( Oncorhynchus nerka Walbaum in Artedi, 1792) have begun spawning migrations weeks earlier than normal, and most perish en route as a result. We suspect that a high midsummer river temperature is the principal cause of mortality. We intercepted 100 sockeye during normal migration near a spawning stream and measured somatic energy and aspects of plasma biochemistry. Fish were then held at either 10 or 18 °C for 24 days. Before release, fish were biopsied again and implanted with acoustic transmitters. A group of biopsied but untreated control salmon were released at the same time. Sixty-two percent (8 of 13) of control salmon and 68% (21 of 31) of 10 °C salmon reached spawning areas. The 18 °C-treated fish were half as successful (35%; 6 of 17). During the holding period, mortality was 2 times higher and levels of Parvicapsula minibicornis (Kent, Whitaker and Dawe, 1997) infection were higher in the 18 °C-treated group than in the 10 °C-treated group. The only physiological difference between treatments was a change in gill Na+,K+-ATPase activity. This drop correlated negatively with travel times for the 18 °C-treated males. Reproductive-hormone levels and stress measures did not differ between treatments but showed significant correlations with individual travel times.

Physiology of individual late-run Fraser River sockeye salmon (Oncorhynchus nerka) sampled in the ocean correlates with fate during spawning migration

Beginning in 1995, segments of the late-run sockeye salmon (Oncorhynchus nerka) stocks from the Fraser River, British Columbia, have initiated upriver spawning migration up to 6 weeks earlier than historical records; and those fish have experienced high rates of en route mortality. We examined the correlations between physiological and energetic status prior to river entry with subsequent migratory performance of individual salmon using telemetry and noninvasive biopsies for Adams–Thompson–Shuswap (Adams) and Weaver–Harrison (W–H) stocks. Salmon that failed to reach the river were characterized by a tendency to have elevated levels of chronic and acute stress indicators. For one stock of fish (i.e., Adams) that entered the river, those that died before reaching spawning grounds were individuals with low gross somatic energy. Furthermore, females tended to have elevated plasma estradiol levels. When contrasting fish with different behaviours and fates, fish that did not hold in the estuary and subsequently died tended to have less energy than fish that held and reached spawning areas. Females from the former group also had higher 11-ketotestosterone and estradiol levels relative to those from the later group. These data suggest that differences in physiological and energetic status may be associated with high en route mortality in late-run sockeye salmon.

Physiological and energetic correlates of en route mortality for abnormally early migrating adult sockeye salmon (Oncorhynchus nerka) in the Thompson River, British Columbia

Since 1995, large segments of the late-run sockeye salmon (Oncorhynchus nerka) stock complex from the Fraser River, British Columbia, Canada, have been initiating spawning migrations several weeks earlier than normal. Most aberrant migrants die before spawning. To evaluate the mechanisms underlying the mortality, we intercepted late-run sockeye salmon of the Adams–Shuswap stock complex halfway along their freshwater migration (i.e., in the Thompson River Canyon situated 270 km from the Fraser estuary), nonlethally assessed physiological and energetic status, and tracked individuals using gastrically inserted radio transmitters. Aberrant migrants that resumed their migration but failed to reach the spawning grounds had lower gross somatic energy, higher average migration ground speeds, higher plasma osmolality, and higher levels of plasma reproductive hormones than those that reached the spawning grounds. Fish surgically fitted with electromyogram radio transmitters did not continue their migration and fell downstream. These fish displayed excessive bleeding during transmitter implantation, an unusual phenomenon that likely contributed to the fish's inability to resume migration. Blood clotting time decreased steadily throughout the migration period. Collectively, these data implicate a combination of energy depletion, premature reproductive development, and blood loss from wounds as potential contributors to mortality in early migrating late-run sockeye.