Rendimiento académico en los estudiantes adolescentes

3.4.1.1.Morphogenesis

The stages of opercular regeneration considered here are illustrated in Fig. 3.1, with the exception of the easy break point, which is discussed below. The timing of morphogenetic events varies among individuals, but usually by no more than 1-2 days (for all morphogenetic landmarks except the easy break point, at least 95% of individuals fell within a 2-day window). Just after amputation at the easy break point, the remaining stump (the proximal half of the peduncle) ends in a triangular wound surface, which rapidly contracts to seal the wound (Fig. 3.1A). By 1 dpo, nearly all (90/96) peduncle stumps display obvious signs of regeneration: the wound has healed over and the corners of the amputation surface are beginning to form into prongs, the stump has grown noticeably longer, and usually, a slight swelling is evident around the middle of the stump (Fig. 3.1B). Around 2 dpo, this swelling enlarges (Fig. 3.1C), then the distal end of the swelling forms a rim, differentiating the future cup from the future spine (Fig. 3.1D). Soon after the rim is apparent, the swelling becomes distinctly cup-shaped with a more noticeable boundary at its base and an expanding, more or less flat, opercular plate at its distal surface (Fig. 3.1E). Calcification normally becomes apparent at this time (Fig. 3.1F), although 13 animals began calcifying before reaching cup stage. The earliest signs of calcification are opaque whitish patches/bands around the base of the spine, and small, scattered, beadlike objects. Under higher magnification, the former can be seen to be composed of micrometre-scale grains, and the latter appear as larger, roughly circular “tiles” (see Chapter 4). Rim and cup formation and calcification generally all occur between 2-3 dpo.

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Figure 3.1. Opercular regeneration in S. lamarcki.All photographs are dorsal views except F, G

and J (left lateral). Scale bars are approximately 0.5 mm. A-H. Stages of morphogenesis. A. Peduncle stump shortly after amputation. The triangular wound surface has contracted. Residual white and brown pigmentation is visible at the end of the stump. B. Regeneration initiated, with stump elongation, developing prongs (arrow) and a small swelling (arrowhead). Pictured specimen is 1 dpo.

C. Strong swelling (2 dpo specimen). D. Rim formation (2 dpo specimen). The distal margin of the swelling (arrowhead) is becoming more distinct from the spine. E. Cup formation. The swelling is clearly cup-shaped, with a plate expanding between rim and spine. Pictured specimen is 2 dpo. F.

Calcification. Small, round tiles are visible around the base of the spine. (Specimen is 2 dpo, cup stage.) G. Groove formation. Peduncle and cup are now separated by a sharp line (arrowhead). The specimen is 5 dpo. H. Wing formation. Wing buds (inset, arrowhead) appear at the distal end of the peduncle (6 dpo specimen). I-J. Development of pigmentation. I. Dotted pigmentation on cup wall (6 dpo). Inset shows close-up of the boxed area with reddish pigment dots. J. 14 dpo specimen displaying all elements of mature pigmentation (dark banding on cup, proximal and distal pigment bands on peduncle, white bands). Pigmentation can darken considerably after this point. K. Timing of morphogenetic and pigmentation stages in 96 adult worms. Boxes represent interquartile ranges with a median line. Whiskers extend to 1.5 IQR. Numbers under the plot indicate the number of specimens that reached each stage within the observation period. The diagrams under each box represent the stages depicted in A-J as indicated by the letters. The easy break point is not included in this figure due to its unreliability as a landmark (see main text). Figure from Szabó and Ferrier (2014a).

The next stage in morphogenesis is the delineation of the peduncle from the cup (i.e. the operculum proper). In the mature opercular filament, the boundary is characterised by a conspicuous groove, which involves an invagination of epidermis and cuticle and a constriction of the mesodermal component of the peduncle (Bubel et al., 1980; 1985). The first external sign of the developing groove, usually apparent by 3-4 dpo, is the sharpening of the previously smooth operculo- peduncular boundary (Fig. 3.1G). The last major morphological landmark (apart from the easy break point, see below) is the appearance of wing buds. The lateral wings are a prominent feature of mature opercular filaments, extending from the distal peduncle on either side of the cup. They are continuations of more or less prominent lateral ridges that contribute to the strongly triangular cross section of the distal peduncle. Wings typically begin development between 4-6 dpo as slight protuberances at the distal end of the peduncle (Fig. 3.1H). With the commencement of wing development, the mature morphology of the opercular filament is essentially complete, although both the entire filament and particular elements of its anatomy (most notably the wings and the calcified opercular plate) continue to grow for several weeks.

3.4.1.2.Pigmentation

When all morphogenetic landmarks are in place, the operculum begins to develop pigmentation. Some pigmentation from the proximal half of the old peduncle is often left after amputation. The first new pigmentation to appear is normally scattered red or brown dots on the wall of the cup, but aside from this, the order of appearance of different elements of pigmentation varies. Likewise, the timing of appearance of most individual components of pigmentation is considerably more variable than that of morphogenetic landmarks (median range 2 days for morphogenetic, 8 days for pigmentation landmarks). In this study, pigmentation was never observed before all morphogenetic landmarks were present.

40 3.4.1.3.Potential factors affecting the time course of regeneration

The rate and success of regeneration can depend on a number of factors; age, here represented by size (Tartakovskaya et al., 2003; Somorjai et al., 2012; Seifert and Voss, 2013; Jeffery, 2014) and sex (Nachtrab et al., 2011) have both been shown to exert an influence in other organisms. Additional injuries, which may represent a drain on an organisms’s resources, are probably not strongly influential in S. lamarcki (S. Miles and D. Ferrier, unpublished), but they were recorded to be certain. Box plots comparing the time course of regeneration in animals of different sexes (female or male), sizes (lower and upper quartile of thorax length), modes of opercular loss (cut or autotomy) and health status (intact or injured during detubing) are shown in Fig. 3.3. None of these factors have a discernible effect on the course of regeneration. Furthermore, although more injured animals produced small imperfections such as subcuticular bubbles (14/27 versus 27/69), this difference is not statistically significant (χ2 _{= 1.28, df = 1, p = 0.25). There were too} few aborted regenerates (n = 7) to test whether injuries or abnormalities are related to regeneration success, but similar numbers of normal (3) and defective (4) regenerates were aborted, and only 2/7 abortions occurred in animals that had been injured during detubing. Examples of regeneration defects are shown in Fig. 3.2. Bubbles are by far the most common defects (33/41 in this sample), and more than a third of all bubbles disappeared within the observation period (13/33).

Figure 3.2. Common defects of opercular regeneration. A. Bubbling of the cuticle (arrow). Right dorsolateral view. B. Short peduncle (left lateral view). C. Laterally kinked peduncle (dorsal view). Anterior is towards the top in all images; scale bars are approximately 0.5 mm.

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Figure 3.3. Comparison of regeneration time courses by potential confounding factors. A. Sex (49 females and 42 males). Five worms did not spawn and could not be sexed. B. Mode of amputation (55 manual, 41 autotomies). C. Size (30 in lower quartile [1.3-2.2 mm], 27 in upper quartile [2.5-3.1 mm] of thorax length). D. Injuries other than opercular amputation (69 intact, 27 injured). Figure adapted from Szabó and Ferrier (2014a).

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