Helix pomatia also Roman snail, Burgundy snail, edible snail or escargot, Extra close up, macro.
Apterona helix - Bugwoodwiki
Close-up video of small snail moving and eating a leaf. Close-up video of small snail in grass. Macro of beautiful snail crawling in nature. Helix pomatia.
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Snail crawling over the tree. Usage Information Video "Helix pomatia, common names Roman snail, Burgundy snail, edible snail or escargot, is species of large, edible, air-breathing land snail, terrestrial pulmonate gastropod mollusk in family Helicidae. We performed a seminatural experiment for measuring phenotypic selection on standard metabolic rate SMR , the minimum cost of maintenance in ectotherm organisms.
FLY WITH RED EYES Helix aspersa GARDEN SNAIL DSC_3635.jpg
Correlational selection was not significant for any possible pair of traits. To the best of our knowledge, this is the first study showing significant directional selection on the obligatory cost of maintenance in an animal, providing support for the energetic definition of fitness. Historically, natural selection has been recognized as the main mechanism explaining adaptive evolution Endler This claim is supported by extensive empirical studies on morphological e.
However, a somewhat unexplored topic in evolutionary biology is the origin of physiological adaptations, for which the demonstrations of phenotypic selection are scarce Endler ; Conner ; Hoekstra et al. One of the most ecologically relevant physiological traits is maintenance metabolism i. Not surprisingly, physiological ecologists have expended considerable effort in studying energy metabolism in a number of animal species and situations Hinds et al. However, despite the apparent importance of energy metabolism and its likely effect on fitness Konarzewski et al.
Certainly, the many logistical obstacles that the measurement of physiological and performance traits entail, combined with the requirements of phenotypic selection experiments i. We tested two contrary arguments that could be invoked to infer the relationship between SMR and fitness. First, SMR could be considered a cost affecting survival, which is a consequence of the energetic definition of fitness i. Thus, it is predictable that directional selection will act to reduce the magnitude of SMR. In this case, correlational selection augmenting the combination of SMR and one or more performance traits would be expected.
Material and Methods
With the goal of testing these hypotheses, we captured, marked, and measured juvenile individuals of the land snail, H. We also determined selection on a proxy of body size. Juveniles of this species can be easily identified by the absence of a thickened lip at the shell aperture, called the peristome, which indicates adulthood Czarnoleski et al.
Relative humidity was maintained at high levels by sprinkling the interior of the boxes with water, daily. Each individual was marked with a small plastic numbered tag and no individual became reproductive during the study period.
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The main trait that we measured was SMR, which is defined as the obligatory energy cost required to support basic life functions McNab , and must be measured in animals at rest and in a post absorptive state without digestion, see below Willmer et al. Respirometric trials were performed during the day, which corresponds to the resting phase in this species Bailey ; Attia et al. In addition, animals were deprived of food for 18 h prior to measurement, which was enough time to attain a postabsorptive state based on preliminary measurements of mean retention time in this species P.
Artacho, T. Nespolo, unpubl. A postabsorptive state is necessary because of the heat increase caused by feeding due to the specific dynamic action of digestion Lighton ; Bradley et al. Also, animal activity was visually monitored at intervals of ca.
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The few recordings of animals that were active during the metabolic measurements were discarded. Although there was almost no drift between calibrations, we performed baseline measurements before and after each recording. Each animal was located in a different, isolated metabolic chamber. We had eight simultaneous metabolic chambers three of which were empty, as blanks.
From the respirometric recordings and based on the configuration of the system i. In addition to energy metabolism, we measured traits that putatively represent performance in an organism such as mean speed MS and maximum force of dislodgement MFD.
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Before each measurement the surface was cleaned to avoid the probable inhibition of locomotion provoked by the mucus left by the previous individual Baur MDF was evaluated, by means of a g dynamometer, as the force necessary to detach the individual from the substrate. One hour before the measurements a small length of nylon thread was attached to the top of the shell with a drop of glue. Individuals were then placed on a glass surface to induce maximum adhesion Trussell A dynamometer was quickly connected to the thread on the snail's shell and slowly pulled up until the individual detached from the substrate.
Finally, two proxies of body size body mass, Mb, and shell size, SS , plus foot length FL and width FW were estimated using digital images. Each individual was measured for SMR, performance, and morphological traits during the same period SMR during day, performance and morphology in the beginning at night. Because individuals were preselected to be of approximately similar body masses, this variable had a low nonsignificant correlation with all traits. Analyses were performed on both, residuals from linear regressions with body mass and on trait values, and results were identical.
At the beginning of the spring, we released all the measured snails in three replicated field enclosures of 64 m 2 snails per enclosure with a density of 1. We determined the survival in the field enclosures at the end of the summer of seven months later. Thus, the period in which we performed the selection experiment corresponds to the end of hibernation and the beginning of the active season. One experimental enclosure was eliminated from the study because it was attacked by rats in the first month of the experiment.
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