Optimización de la respuesta a la selección artificial

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Biológicas, leída en 1984.Fac. de Ciencias BiológicasTRUEProQuestpu

Optimización de la respuesta a la selección artificial

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Biológicas, leída en 1984.Fac. de Ciencias BiológicasTRUEProQuestpu

Genetic purging in captive endangered ungulates with extremely low effective population sizes

Inbreeding threatens the survival of small populations by producing inbreeding depression, but also exposes recessive deleterious effects in homozygosis allowing for genetic purging. Using inbreeding-purging theory, we analyze early survival in four pedigreed captive breeding programs of endangered ungulates where population growth was prioritized so that most adult females were allowed to contribute offspring according to their fitness. We find evidence that purging can substantially reduce inbreeding depression in Gazella cuvieri (with effective population size Ne = 14) and Nanger dama (Ne = 11). No purging is detected in Ammotragus lervia (Ne = 4), in agreement with the notion that drift overcomes purging under fast inbreeding, nor in G. dorcas (Ne = 39) where, due to the larger population size, purging is slower and detection is expected to require more generations. Thus, although smaller populations are always expected to show smaller fitness (as well as less adaptive potential) than larger ones due to higher homozygosis and deleterious fixation, our results show that a substantial fraction of their inbreeding load and inbreeding depression can be purged when breeding contributions are governed by natural selection. Since management strategies intended to maximize the ratio from the effective to the actual population size tend to reduce purging, the search for a compromise between these strategies and purging could be beneficial in the long term. This could be achieved either by allowing some level of random mating and some role of natural selection in determining breeding contributions, or by undertaking reintroductions into the wild at the earliest opportunity

Evolution de l'effectif génétique de lignées de Drosophila melanogaster soumises à une sélection artificielle

International audienc

Reviewing the consequences of genetic purging on the success of rescue programs

Genetic rescue is increasingly considered a promising and underused conservation strategy to reduce inbreeding depression and restore genetic diversity in endangered populations, but the empirical evidence supporting its application is limited to a few generations. Here we discuss on the light of theory the role of inbreeding depression arising from partially recessive deleterious mutations and of genetic purging as main determinants of the medium to long-term success of rescue programs. This role depends on two main predictions: (1) The inbreeding load hidden in populations with a long stable demography increases with the efective population size; and (2) After a population shrinks, purging tends to remove its (partially) recessive deleterious alleles, a process that is slower but more efcient for large populations than for small ones. We also carry out computer simulations to investigate the impact of genetic purging on the medium to long term success of genetic rescue programs. For some scenarios, it is found that hybrid vigor followed by purging will lead to sustained successful rescue. However, there may be specifc situations where the recipient population is so small that it cannot purge the inbreeding load introduced by migrants, which would lead to increased ftness inbreeding depression and extinction risk in the medium to long term. In such cases, the risk is expected to be higher if migrants came from a large non-purged population with high inbreeding load, particularly after the accumulation of the stochastic efects ascribed to repeated occasional migration events. Therefore, under the specifc deleterious recessive mutation model considered, we conclude that additional caution should be taken in rescue programs. Unless the endangered population harbors some distinctive genetic singularity whose conservation is a main concern, restoration by continuous stable gene fow should be considered, whenever feasible, as it reduces the extinction risk compared to repeated occasional migration and can also allow recolonization events

Sol-gel coatings for protection and bioactivation of metals used in orthopaedic devices

The aim of this work is the production and characterisation of sol-gel coatings for protection and bioactivation of metals used as standard surgical implant materials, such as stainless steel 316 L (ASTM F138), Co based alloys (ASTM F75) and titanium alloy Ti-6A1-4V (ASTM F67). These films should both prevent degradation of the substrates by wear or corrosion, and bioactivate the material for inducing the formation of a hydroxyapatite (HA) rich layer onto the material surface, thereby permitting a natural bonding to living tissues. Formation of HA layers can be observed on performing in vitro tests by soaking the material in simulated body solutions. The work describes the development of coatings containing bioactive glass and glass-ceramic particles in hybrid methyl-triethoxysilane (MTES) and tetraethylorthosilicate (TEOS) acidic sol, applied by dip-coating to surgical alloys, AISI 316 L, ASTM F75 and ASTM 67, with the aim of accomplishing both high corrosion resistance of the metal in the body environment and adhesion of the implant to the surrounding tissue. The performance of the coated metal was evaluated in vitro by electrochemical techniques including potentiodynamic polarisation curves and electrochemical impedance spectroscopy, to follow the formation of hydroxyapatite on the surface, as well as the in vitro release of ions by plasma atomic emission spectroscopy (ICP-MS) after up to one year of immersion. In vivo behaviour was evaluated by subcutaneous tests and endomedullar implantation in Hokaido rats to study possible rejection reactions and natural bonding to living tissue.Peer Reviewe

Long-term exhaustion of the inbreeding load in Drosophila melanogaster

Inbreeding depression, the decline in fitness of inbred individuals, is a ubiquitous phenomenon of great relevance in evolutionary biology and in the fields of animal and plant breeding and conservation. Inbreeding depression is due to the expression of recessive deleterious alleles that are concealed in heterozygous state in noninbred individuals, the so-called inbreeding load. Genetic purging reduces inbreeding depression by removing these alleles when expressed in homozygosis due to inbreeding. It is generally thought that fast inbreeding (such as that generated by full-sib mating lines) removes only highly deleterious recessive alleles, while slow inbreeding can also remove mildly deleterious ones. However, a question remains regarding which proportion of the inbreeding load can be removed by purging under slow inbreeding in moderately large populations. We report results of two long-term slow inbreeding Drosophila experiments (125–234 generations), each using a large population and a number of derived lines with effective sizes about 1000 and 50, respectively. The inbreeding load was virtually exhausted after more than one hundred generations in large populations and between a few tens and over one hundred generations in the lines. This result is not expected from genetic drift alone, and is in agreement with the theoretical purging predictions. Computer simulations suggest that these results are consistent with a model of relatively few deleterious mutations of large homozygous effects and partially recessive gene actionAgencia Estatal de Investigación (AEI) | Ref. PGC2018-095810-B-I00Agencia Estatal de Investigación (AEI) | Ref. PID2020-114426GB-C21Xunta de Galicia | Ref. ED431C 2020-0

Purging of deleterious burden in the endangered Iberian lynx

Deleterious mutations continuously accumulate in populations, building up a burden that can threaten their survival, particularly in small populations when inbreeding exposes recessive deleterious effects. Notwithstanding, this process also triggers genetic purging, which can reduce the deleterious burden and mitigate fitness inbreeding depression. Here, we analyzed 20 whole genomes from the endangered Iberian lynx and 28 from the widespread Eurasian lynx, sister species which constitute a good model to study the dynamics of deleterious mutation burden under contrasting demographies, manifested in the consistently smaller population size and distribution area of the Iberian lynx. We also derived analytical predictions for the evolution of the deleterious burden following a bottleneck. We found 11% fewer derived alleles for the more putatively deleterious missense category in the Iberian lynx than in the Eurasian lynx, which, in light of our theoretical predictions, should be ascribed to historical purging. No signs of purging were found in centromeres nor in the X chromosome, where selection against recessive deleterious alleles is less affected by demography. The similar deleterious burden levels for conspecific populations despite their contrasting recent demographies also point to sustained differences in historical population sizes since species divergence as the main driver of the augmented purging in the Iberian lynx. Beyond adding to the ongoing debate on the relationship between deleterious burden and population size, and on the impact of genetic factors in endangered species viability, this work contributes a whole-genome catalog of deleterious variants, which may become a valuable resource for future conservation efforts

Simulation of the evolution of inbreeding load under partial selfing

Starting with allele frequencies corresponding to the mutation-selection balance, this program simulates the evolution of independent loci under mutation and selection in populations with N monoecious individuals. These populations are run for t generations (generaciones) assuming a given selfing rate. The inbreeding load is computed as B=Σ2dpq (the addition is over loci; see article), and its value at the Mutation-Selection-Drift-Inbreeding balance must be obtained by averaging B over a number of generations well after it reached a plateau. Values were averaged over a number of simulation replicates (repeticiones)