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Parasites and Conservation Biology
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
Some host populations by virtue of suffering losses in numbers consequently experience loss of genetic diversity. This diversity is needed to withstand both short-term environmental perturbations and, on longer time scales, to evolve in response to environmental changes (recall the example of the Hawaii ‘amakihi and ‘i’iwi mentioned earlier). Small host populations can lose genetic diversity as a result of random events (genetic drift; see Chapter 7) or as a consequence of inbreeding if the diversity of potential mates is limited. Inbreeding refers to reproduction by mates who are closely related, which leads to homozygosity, loss of genetic diversity and increased chances that offspring can be affected by deleterious traits. Inbreeding depression refers to the loss of fitness in a population from the breeding of related individuals.
The Reproductive Systems of Davidson’s Plum (Davidsonia jerseyana, Davidsonia pruriens and Davidsonia johnsonii) and the Potential for Domestication
Published in Yasmina Sultanbawa, Fazal Sultanbawa, Australian Native Plants, 2017
Frances Eliott, Mervyn Shepherd, Maurizio Rossetto, Robert Henry
Another reason to suspect long-term selfing in D. jerseyana is that inbreeding depression was not apparent in offspring included in fitness trials (see the following) and inbreeding depression is more common in predominantly selfing populations of naturally outcrossing species (Stebbins, 1950). Inbreeding depression results in a reduction in offspring fitness and is caused by increased homozygosity in individuals which can effectively ‘fix’ recessive deleterious mutations in populations or an increase in homozygosity at loci with heterozygote advantage (‘overdominance’) (Charlesworth and Willis, 2009). With prolonged selfing, these deleterious alleles can be purged from a population through selection (Charlesworth and Charlesworth, 1987; Lande and Schemske, 1985), whereby individuals with the lethal allele may not reach reproductive age and as a consequence, the allele is not passed on and is eventually purged from the population. Thus, over a period of time and if the population does not vanish as a consequence of inbreeding, the effects of inbreeding depression are greatly reduced or even eliminated.
Parasites and Conservation Biology
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2015
Eric S. Loker, Bruce V. Hofkin
Some host populations by virtue of suffering losses in numbers consequently experience loss of genetic diversity. This diversity is needed to withstand both short-term environmental perturbations and, on longer time scales, to evolve in response to environmental changes (recall the example of the Hawaii ‘amakihi mentioned earlier). Small host populations can lose genetic diversity as a result of random events (genetic drift; see Chapter 7) or as a consequence of inbreeding if the diversity of potential mates is limited. Inbreeding refers to reproduction by mates who are closely related, which leads to homozygosity, loss of genetic diversity, and increased chances that offspring can be affected by deleterious traits. Inbreeding depression refers to the loss of fitness in a population from the breeding of related individuals. Loss of genetic diversity might have a general effect that ultimately limits the ability of individuals in the population to mount effective immune responses or it might more specifically affect immune genes directly responsible for recognizing and resisting parasites. For instance, recall from Chapter 4 that proteins encoded by loci of the major histocompatibility complex (MHC) play a major role in antigen presentation in the vertebrate adaptive immune response. MHC genes are highly polymorphic and many variant alleles are present in a typical population. Although we noted in Chapters 4 and 7 that optimal (rather than maximal) levels of MHC diversity might be selected for within individuals, if a population lacks genetic diversity, its repertoire of MHC alleles may be limited, potentially limiting its ability to present antigens derived from some parasites. The relative roles of general inbreeding depression, and of reduced diversity in specific immune loci such as the MHC are often not teased apart in conservation studies of species endangered by parasite attack.
Consequence of emergence pattern on inbreeding risk in the aphid parasitoid Aphidius matricariae (Hymenoptera: Braconidae)
Published in Chronobiology International, 2019
Delphine Bourdais, Thierry Hance
In insect parasitoids, numerous life history traits are host-constrained (Hance et al. 2007). For instance, mating depends on the spatial distribution of the host and the way female distributes eggs inside the host population (Boulton et al. 2015; Godfray 1994; Wajnberg 2006). Females of solitary species usually lay a single egg in each solitary host and newly emerged adults must disperse from their natal patch to find a mate (Godfray and Cook 1997). In such species, competition for mates is ubiquitous for all individuals throughout the whole population. Conversely, in solitary parasitoids that develop in a quasi-gregarious fashion (when females lay a single egg per host and hosts are clumped) and gregarious parasitoids (when females lay several eggs in each solitary host), emerging together on the natal patch facilitates the finding of a partner and saves time. Thus, adults may mate totally or partially on their natal patch (Boulton et al. 2015; Hamilton 1967; Le Ralec et al. 2010; Wajnberg 2006). However, it increases the competition between brothers to mate with their sisters (Local Mate Competition, LMC, Hamilton; 1967; Werren 1980) and the probability for inbreeding (Beck 1991; Doyon and Boivin 2005), situation already described by Hamilton in 1967 as extreme biofacies. So, for species presenting a risk of inbreeding depression, selection should lead to the avoidance of mating on the emergence patch. Partners may mate with non-related individuals if they are able to distinguish them. Otherwise, we can expect a rapid dispersal of the emergence zone. The study of emergence patterns and the time spent by male and females on the place of emergence may thus provide interesting insights on the mating structure in this case.
A report of congenital adrenal hyperplasia due to 17α-hydroxylase deficiency in two 46,XX sisters
Published in Gynecological Endocrinology, 2020
Fernando Espinosa-Herrera, Estefanía Espín, Ana M. Tito-Álvarez, Leonardo-J Beltrán, Diego Gómez-Correa, German Burgos, Arianne Llamos, Camilo Zurita, Samantha Rojas, Iván Dueñas-Espín, Kenny Cueva-Ludeña, Jorge Salazar-Vega, Jorge Pinto-Basto
Besides, rarer autosomal recessive genetic diseases have been detected in the Ecuadorian population of Loja province; alluding a probable inbreeding depression attributable to the small size of the population and its endogamy practices [13]. This finding is in accordance with a Mexican study, wherein three identified cases of 17OHD originate from small, rural communities with consanguinity manifestations [6].
Is the “Habsburg jaw” related to inbreeding?
Published in Annals of Human Biology, 2019
Román Vilas, Francisco C. Ceballos, Laila Al-Soufi, Raúl González-García, Carlos Moreno, Manuel Moreno, Laura Villanueva, Luis Ruiz, Jesús Mateos, David González, Jennifer Ruiz, Aitor Cinza, Florencio Monje, Gonzalo Álvarez
In order to evaluate the impact of inbreeding on MD and MP, the inbreeding coefficient (F) computed from a large-scale family tree of the Habsburgs, which included more than 6000 individuals belonging to more than 20 parent–offspring generations, was used (Álvarez and Ceballos 2015). The relation of the facial deformity, whether defined as MP or MD, with F was studied by treating both traits as quantitative characters. Considering a single diallelic locus (B) involved in facial deformity where B2 allele increases facial deformity with respect to the B1 allele, and using the scale of genotypic values: 0 for B1B1; 1B2 and 2a for B2B2, where a is the additive effect and k provides a measure of dominance, the change in mean value in an inbred population relative to a panmictic population is: p and q are the frequencies of the alleles B1 and B2, respectively (Lynch and Walsh 1998). If there is no dominance and B1 and B2 alleles are completely additive (k = 0), the change of mean value due to inbreeding is not expected. If the B2 allele, which increases facial deformity, is completely dominant (k = 1), a reduction in facial deformity is expected under inbreeding. On the contrary, if the B2 allele is completely recessive (k = −1), an increase in facial deformity (i.e. inbreeding depression) should be found. Considering all the loci that affect the trait, the total inbreeding effect is ki may vary from locus to locus, the occurrence of significant inbreeding depression requires directional dominance (Falconer and Mackay 1996; Lynch and Walsh 1998). Note that k = d/a, where d is the measure of dominance in the Falconer’s scale.