LEARNING The objectives of BIOS 781 are to present: OBJECTIVES: 1. basic population and quantitative genetic principles, including classical genetics, chromosomal theory of inheritance, and meiotic recombination 2. an exposure to QTL mapping methods of complex quantitative traits and linkage methods to detect co-segregation with disease 3. methods for assessing marker-disease linkage disequilibrium, including case-control approaches 4. methods for genome-wide association and stratification control.

Genetic Data Analysis

The biological diversity of the planet is being rapidly depleted due to the direct and indirect consequences of human activity. As the size of animal and plant populations decreases, loss of genetic diversity reduces their ability to adapt to changes in the environment, with inbreeding and reduced fitness inevitable consequences for most species. This textbook provides a clear and comprehensive introduction to genetic principles and practices involved in conservation. Topics covered include: • evolutionary genetics of natural populations • loss of genetic diversity in small populations • inbreeding and loss of fitness • population fragmentation • resolving taxonomic uncertainties • genetic management of threatened species • contributions of molecular genetics to conservation. The text is presented in an easy-to-follow format, with main points and terms clearly highlighted. Each chapter concludes with a concise summary, which, together with worked examples and problems and answers, illuminates the key principles covered. Text boxes containing interesting case studies and other additional information enrich the content throughout, and over 100 beautiful pen-and-ink drawings help bring the material to life.

Introduction to Conservation Genetics: Frontmatter

Salinity and its variations are among the key factors that affect survival, metabolism and distribution during the fish development. The successful establishment of a fish species in a given habitat depends on the ability of each developmental stage to cope with salinity through osmoregulation. It is well established that adult teleosts maintain their blood osmolality close to 300 mosM kg−1 due to ion and water regulation effected at several sites: tegument, gut, branchial chambers, urinary organs. But fewer data are available in developing fish. We propose a review on the ontogeny of osmoregulation based on studies conducted in different species. Most teleost prelarvae are able to osmoregulate at hatch, and their ability increases in later stages. Before the occurrence of gills, the prelarval tegument where a high density of ionocytes (displaying high contents of Na+/K+-ATPase) is located appears temporarily as the main osmoregulatory site. Gills develop gradually during the prelarval stage along with the numerous ionocytes they support. The tegument and gill Na+/K+-ATPase activity varies ontogenetically. During the larval phase, the osmoregulatory function shifts from the skin to the gills, which become the main osmoregulatory site. The drinking rate normalized to body weight tends to decrease throughout development. The kidney and urinary bladder develop progressively during ontogeny and the capacity to produce hypotonic urine at low salinity increases accordingly. The development of the osmoregulatory functions is hormonally controlled. These events are inter-related and are correlated with changes in salinity tolerance, which often increases markedly at the metamorphic transition from larva to juvenile. In summary, the ability of ontogenetical stages of fish to tolerate salinity through osmoregulation relies on integumental ionocytes, then digestive tract development and drinking rate, developing branchial chambers and urinary organs. The physiological changes leading to variations in salinity tolerance are one of the main basis of the ontogenetical migrations or movements between habitats of different salinity regimes.

Ontogeny of osmoregulation in postembryonic fish: a review.

Publisher Summary This chapter defines important considerations in the use of condition indices as applied to marine fish larvae, and describes the present state of knowledge concerning each index. An appraisal of their relative merits is then attempted by comparing the strengths and limitations of each category. Measures of condition integrate feeding success over time, and give an indication of the probability of starvation and survival. This chapter explores that, the central purpose of measuring condition is to predict reliably survival probabilities under given food regimes in order that observed larval abundances can be used as early predictors of recruitment. The chapter illustrates that, future research on condition indices is likely to be more productive if it is devoted to the refinement of existing methods, rather than to search for the ideal condition index. The chapter concludes by providing suggestions for the use of condition indices in different situations and identifies topics requiring further research.

An Appraisal of Condition Measures for Marine Fish Larvae

Connective tissues (CTs), which define bodily shape, must respond quickly, robustly and reversibly to deformations caused by internal and external stresses. Fibrillar (elastin, collagen) elasticity under tension depends on molecular and supramolecular mechanisms. A second intra-/inter-molecular pair, involving proteoglycans (PGs), is proposed to cope with compressive stresses. PG interfibrillar bridges (‘shape modules’), supramolecular structures ubiquitously distributed throughout CT extracellular matrices (ECMs), are examined for potential elastic properties. l-iduronate residues in shape module decoran PGs are suggested to be molecular springs, cycling through alternative conformations. On a larger scale, anionic glycosaminoglycan (AGAG) interfibrillar bridges in shape modules are postulated to take part in a sliding filament (dashpot-like) process, which converts local compressions into disseminated tensile strains. The elasticity of fibrils and AGAGs, manifest at molecular and larger-scale levels, provides a graduated and smooth response to stresses of varying degrees. NMR and rheo NMR, computer modelling, electron histochemical, biophysical and chemical morphological evidence for the proposals is reviewed.

Elasticity in extracellular matrix ‘shape modules’ of tendon, cartilage, etc. A sliding proteoglycan‐filament model

Various observations on the morphology, physiology and biochemistry of leptocephalous larvae of different groups of marine teleost fishes have been brought together in order to arrive at a model which attempts to explain the ‘leptocephalous strategy’ of larval development. The observation that basic similarities are found in the developmental pattern of all groups of fishes with a leptocephalus (Superorder: Elopomorpha) forms the basis for proposing a common strategy within the superorder. Circumstantial evidence suggesting that premetamorphic (Phase I) larvae obtain a significant fraction of their nutritional needs by absorbing dissolved organic matter across surface epithelia has been reviewed. It is suggested that this might occur via a Na+-mediated transport system similar to that seen in various marine invertebrates. Breakdown of the gelatinous matrix formed during Phase I is assumed to provide the nutrients required for the metamorphic larvae (Phase II). This strategy is then contrasted with the more ‘typical’ form of larval development in marine teleosts and shown to differ in several basic respects.

Towards an explanation of the developmental strategy in leptocephalous larvae of marine teleost fishes

Energy use and changes in whole-body content of lipid, protein, nitrogen, carbohydrate and ash were followed during metamorphosis of leptocephalous larvae of the bonefish (Albula). During metamorphosis, which requires about 8–12 days, larvae lost about 3–4 mg of lipid, or about 50% of the total lipid content. Lipid levels, calculated on a dry weight basis, showed no discernible trends, with values ranging from 138–185 mg (g dry wt)−1. Protein content was 8.4 mg per larva and showed no significant change. However, protein levels increased from 147 to 329 mg (g dry wt)−1. Nitrogen content decreased slightly from about 3.5 to 3.2 mg per larva. A comparison of protein and nitrogen values, expressed as % dry weight, showed that, in larvae which were just beginning to metamorphose, 70% of the total nitrogen was non-protein nitrogen (NPN). The NPN decreased to 58% of the total nitrogen towards the end of metamorphosis. Carbohydrate content fell from about 3.5 to 0.6 mg per larva, which represents an 83% loss. Carbohydrate levels also fell from about 81 to 32 mg (g dry wt)−1. In addition, most of the carbohydrate appears to be bound to protein. Ash content decreased by 52%, from 4.6 to 2.2 mg per larva. Caloric content fell slightly from about 182 to 141 calories per larva whereas caloric density showed no discernible trends, with values ranging from 4.180 to 4.725 kcal (g dry wt)−1. These results indicate that metamorphosing leptocephali, which apparently do not feed, probably derive most of their energy requirements from metabolizing endogenous lipid and carbohydrate stores formed during the premetamorphic interval.

Changes in biochemical composition and energy utilization during metamorphosis of leptocephalous larvae of the bonefish (Albula)

The desert stream-dwelling fish Poeciliopsis monacha is exposed to extreme seasonal and spatial variation in physical stresses. We examined four diallelic gene loci (Ldh-1, Idh-2, Pgd, and Ck-A) in P. monacha and tested whether genotypes were associated with differential survival of individuals exposed to acute stress. For each locus, the common allele was associated with higher survival during heat and hypoxic stress, whereas the alternate allele was associated with higher survival during cold stress. In most cases, survival of heterozygotes was intermediate and they exhibited less variance in survival than corresponding homozygotes. Identification of sub- stantial linkage disequilibrium in these fish confounds our ability to discern whether the allozymes are the direct targets of selection, or if they just mark chromosomal regions that contain the true modifiers of survival. Nevertheless, the present results clearly identified balancing processes that can serve to stabilize genetic polymorphism in this species.

Balancing selection in a desert stream-dwelling fish, poeciliopsis monacha.

Salinity tolerance of leptocephalous larvae and juveniles of the bonefish (Albulidae:Albula) from the Gulf of California

The leptocephalous larval stages of the bonefish (Albulidae: Albula) are abundant in the coastal regions and hypersaline lagoons (esteros) throughout the Gulf of California during winter and spring. Inshore movements of leptocephali were studied by sampling the entrance to Estero Miramar, at Guaymas, Sonora, Mexico, from February to May, 1981. Thirty-three samples were taken at various times during flood tide. All but four of the samples were taken after sunset. Leptocephali were collected in all months except May. The results suggest that leptocephali enter the estero only during the first few hours of flood tide. Large numbers of larvae were observed during the day at ebb tide maintaining their near-shore position in the entrance channel. These larvae did not appear to be migrating into the estero. This, together with the absence of larvae in daytime samples, suggests that the migration is nocturnal. Most of the 667 leptocephali collected during the sampling period had completed larval growth or were just beginning the metamorphic interval. The median standard length (SL) was 61 mm and the mode was 62 mm. The largest leptocephali measured 71 mm SL. Since metamorphosis is accompanied by a decrease in length, it was concluded that the maximum size attained during larval growth is about 71 mm SL.

Edward Pfeiler

Papers

Towards an explanation of the developmental strategy in leptocephalous larvae of marine teleost fishes

Changes in biochemical composition and energy utilization during metamorphosis of leptocephalous larvae of the bonefish (Albula)

Balancing selection in a desert stream-dwelling fish, poeciliopsis monacha.

Salinity tolerance of leptocephalous larvae and juveniles of the bonefish (Albulidae:Albula) from the Gulf of California

Inshore migration, seasonal distribution and sizes of larval bonefish, Albula, in the Gulf of California