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Longer Development Times (longer + development_time)
Selected AbstractsFITNESS COSTS OF INSECTICIDE RESISTANCE IN NATURAL BREEDING SITES OF THE MOSQUITO CULEX PIPIENSEVOLUTION, Issue 1 2004Denis Bourguet Abstract Genetic changes conferring adaptation to a new environment may induce a fitness cost in the previous environment. Although this prediction has been verified in laboratory conditions, few studies have tried to document this cost directly in natural populations. Here, we evaluated the pleiotropic effects of insecticide resistance on putative fitness components of the mosquito Culex pipiens. Experiments using different larval densities were performed during the summer in two natural breeding sites. Two loci that possess alleles conferring organophosphate (OP) resistance were considered: ace-1 coding for an acetylcholinesterase (AChE1, the OP target) and Ester, a "super locus" including two closely linked loci coding for esterases A and B. Resistance ace-1 alleles coding for a modified AChE1 were associated with a longer development time and shorter wing length. The pleiotropic effects of two resistance alleles Ester1 and Ester4 coding for the overproduced esterases A1 and A4-B4, respectively, were more variable. Both A1 and A4-B4 reduced wing length, although only A1 was associated with a longer preimaginal stage. The fluctuating asymmetry (FA) of the wing did not respond to the presence or to the interaction of resistance alleles at the two loci at any of the density levels tested. Conversely, the FA of one wing section decreased when larval density increased. This may be the consequence of selection against less developmentally stable individuals. The results are discussed in relation to the local evolution of insecticide resistance genes. [source] DIFFERENTIAL SELECTION TO AVOID HYBRIDIZATION IN TWO TOAD SPECIESEVOLUTION, Issue 9 2002Karin S. Pfennig Abstract., The fitness consequences of hybridization critically affect the speciation process. When hybridization is costly, selection favors the evolution of prezygotic isolating mechanisms (e.g., mating behaviors) that reduce heter-ospecific matings and, consequently, enhance reproductive isolation between species (a process termed reinforcement). If, however, selection to avoid hybridization differs between species, reinforcement may be impeded. Here, we examined both the frequency and fitness effects of hybridization between plains spadefoot toads (Spea bombifrons) and New Mexico spadefoot toads (S. multiplicata). Hybridization was most frequent in smaller breeding ponds that tend to be ephemeral, and heterospecific pairs consisted almost entirely of S. bombifrons females and S. multiplicata males. Moreover, in controlled experimental crosses, hybrid offspring from crosses in which S. multiplicata was maternal had significantly lower survival and longer development time than pure S. multiplicata offspring. By contrast, hybrid offspring from crosses in which S. bombifrons was maternal outperformed pure S. bombifrons offspring by reaching metamorphosis faster. These data suggest that, although S. multiplicata females are under selection to avoid hybridization, selection might favor those S. bombifrons females that hybridize with S. multiplicata if their breeding pond is highly ephemeral. Generally, the strength of selection to avoid hybridization may differ for hybridizing species, possibly impeding reinforcement. [source] Small-scaled geographical variation in life-history traits of the blowfly Calliphora vicina between rural and urban populationsENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2009C. C. Hwang Abstract The impact of the urban heat-island effect, the warming-up of an urban area caused by human activity, on the blowfly Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) was examined at two British sites, 30 km apart. Waterloo in Central London is a highly urbanised built-up area, whereas Box Hill in the county of Surrey is a rural pasture and woodland location. The phenotypic plasticity of 12 C. vicina cultures, originated from single females from each of the two sites, was measured using three developmental characters: adult body size (represented as the length of the cross vein dm-cu of the right wing), development time as accumulated degree-days (ADD), and growth rate (length of dm-cu/ADD), along a constant temperature series of 16, 20, 24, and 28 °C in the laboratory. The blowflies from Box Hill had the same ADD as those from Waterloo, but showed a significantly larger adult size and growth rate at lower temperatures, suggesting the existence of local adaptations that may be caused by the differing levels of urbanisation between the two studied sites. Not surprisingly, a trade-off between adult size and development time was found. Females showed longer development times than males at all four temperatures, indicating they may need to ingest more food as larvae to furnish ovarioles and increase fecundity. However, females had larger adult size than males at 16 and 20 °C but a reverse at 28 °C, suggesting that females may be more cold-adapted than males. [source] Thermal evolution of pre-adult life history traits, geometric size and shape, and developmental stability in Drosophila subobscuraJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2006M. SANTOS Abstract Replicated lines of Drosophila subobscura originating from a large outbred stock collected at the estimated Chilean epicentre (Puerto Montt) of the original New World invasion were allowed to evolve under controlled conditions of larval crowding for 3.5 years at three temperature levels (13, 18 and 22 °C). Several pre-adult life history traits (development time, survival and competitive ability), adult life history related traits (wing size, wing shape and wing-aspect ratio), and wing size and shape asymmetries were measured at the three temperatures. Cold-adapted (13 °C) populations evolved longer development times and showed lower survival at the highest developmental temperature. No divergence for wing size was detected following adaptation to temperature extremes (13 and 22 °C), in agreement with earlier observations, but wing shape changes were obvious as a result of both thermal adaptation and development at different temperatures. However, the evolutionary trends observed for the wing-aspect ratio were inconsistent with an adaptive hypothesis. There was some indication that wing shape asymmetry has evolutionarily increased in warm-adapted populations, which suggests that there is additive genetic variation for fluctuating asymmetry and that it can evolve under rapid environmental changes caused by thermal stress. Overall, our results cast strong doubts on the hypothesis that body size itself is the target of selection, and suggest that pre-adult life history traits are more closely related to thermal adaptation. [source] Which Tangible and Intangible Assets Matter for Innovation Speed in Start-Ups?,THE JOURNAL OF PRODUCT INNOVATION MANAGEMENT, Issue 4 2007Ans Heirman The launch of the first product is an important event for start-ups, because it takes the new venture closer to growth, profitability, and financial independence. The new product development (NPD) literature mainly focuses its attention on NPD processes in large firms. In this article insights on the antecedents on innovation speed in large firms are combined with resource-based theory and insights from the entrepreneurship literature to develop hypotheses concerning the antecedents of innovation speed in start-ups. In particular, tangible assets such as starting capital and the stage of product development at founding and intangible assets such as team tenure, experience of founders, and collaborations with third parties are considered as important antecedents for innovation speed in start-ups. A unique data set on research-based start-ups (RBSUs) was collected, and event-history analyses were used to test the hypotheses. The rich qualitative data on the individual companies are used to explain the statistical findings. This article shows that RBSUs differ significantly in their starting conditions. The impact of starting conditions on innovation speed differs between software and other companies. Although intuition suggests that start-ups that are further in the product development cycle at founding launch their first product faster, our data indicate that software firms starting with a beta version experience slower product launch. The amount of initial financing has no significant effect on innovation speed. Next, it is shown that team tenure and experience of founders leads to faster product launch. Contrary to expectations, alliances with other firms do not significantly affect innovation speed, and collaborations with universities are associated with longer development times. [source] | ||||||||||