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206 results for “cline”

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dryad32/100

Repeated elevational clines of early life-history traits and their proximate mechanisms in brown trout

1. Climate warming imposes a severe threat to freshwater ecosystems, which are dominated by ectotherms such as fish and aquatic insects. To better predict the effects of climate warming on thermally sensitive ecosystems, information on how temperature affects individual traits within populations is fundamental. 2. Patterns of intraspecific variation in thermal reaction norms along geographic thermal gradients provide valuable information. Immediate temperature effects on individual traits can be inferred from the shape of the thermal reaction norm. The way that temperature and associated environmental conditions (to which populations have been exposed over generations) affect individual traits through transgenerational plasticity in, and/or natural selection on, these traits can also be inferred from patterns of trait variation along a geographic thermal gradient. 3. Many studies have documented patterns of intraspecific variation in thermal reaction norms along geographic thermal gradients. However, most previous studies cannot exclude the possibility that the observed geographic patterns are solely explained by random processes, such as isolation by distance, due to the lack of replication of geographic gradients. Here, we show consistent patterns in intraspecific trait variation along geographic thermal gradients using Salmo trutta (brown trout), which is an ecologically and economically important fish in alpine streams. 4. We kept trout embryos collected from 52 families from 14 populations along wide and replicated elevational gradients from three Alpine drainages (Danube, Po, and Rhine) in two temperature treatments (3.2 and 6.2 °C). Timing and body size at emergence from the nest, which are key early life-history traits of trout affecting their early growth and survival, were measured. 5. Besides faster embryonic development at warmer temperatures, we found that offspring from low-elevation parents took very slightly more days to reach emergence from fertilisation and were larger than offspring from high-elevation parents. Importantly, this was evident for all three drainages. Further analyses found that the higher number of days until- and larger body length at- emergence of low-elevation trout were mainly due to the larger eggs laid by low-elevation females, which had larger body size than high-elevation females. 6. Trout female body size, which is positively correlated with egg size, is susceptible to temperatures and associated environmental conditions. Consequently, climate warming may not only immediately accelerate development rate but also shift timing and size at emergence through egg-size-mediated maternal effects within a relatively short time scale.

opencc-zeroFeb 2023View details →

dryad32/100

Horseshoe crab body size cline

Aim Adult body size often exhibits patterns across large-scale environmental gradients, creating ecogeographic clines. However, the form of body size clines varies across taxonomic groups, with linear and non-linear patterns in body size observed in nature. Non-linear body size clines have received less study, and questions remain about how environmental gradients interact to produce non-linear clines. We examined the body size of the American horseshoe crab (Limulus polyphemus), a widely distributed marine arthropod, and evaluated the hypothesis that temperature and active season length can interact multiplicatively to result in a dome-shaped distribution. Location Fourteen states in the United States of America and three Mexican states, representing the entire geographic range of the species. Methods We compiled environmental data and body size measurements from more than 49,000 individual horseshoe crabs. For each location, we extracted from the literature or calculated from raw data the mean male prosoma width and the mean female prosoma width. We applied a General Additive Modeling (GAM) approach to characterize the body size cline, test a hypothesis regarding temperature and season length, and explore evidence for the influence of additional environmental factors. Results Model results indicate temperature and season length could act multiplicatively to produce dome-shaped clines, and these findings align with and quantify previous anecdotal reports of a strong dome-shaped body size cline across latitude for horseshoe crabs. Main conclusions Active season length appears to become relatively more influential on horseshoe crab body size in the northern part of their range, while temperature effects per se appear to dominate in southern latitudes. For horseshoe crabs, the pattern of size variation is consistent with the predictions of Optimal Resource Allocation models, but more study is needed to elucidate mechanistic underpinnings. Considering climate change projections, results from our study suggest future shifts in horseshoe crab body sizes.

opencc-zeroSep 2023View details →

dryad32/100