Quantitative genetics of taura syndrome resistance in pacific white shrimp (penaeus vannamei): a cure model approach

<p>Abstract</p> <p>Background</p> <p>In aquaculture breeding, resistance against infectious diseases is commonly assessed as time until death under exposure to a pathogen. For some diseases, a fraction of the individuals may appear as "cured" (non-susceptible), and the resulting survival time may thus be a result of two confounded underlying traits, i.e., endurance (individual hazard) and susceptibility (whether at risk or not), which may be accounted for by fitting a cure survival model. We applied a cure model to survival data of Pacific white shrimp (<it>Penaeus vannamei</it>) challenged with the Taura syndrome virus, which is one of the major pathogens of Panaeid shrimp species.</p> <p>Methods</p> <p>In total, 15,261 individuals of 513 full-sib families from three generations were challenge-tested in 21 separate tests (tanks). All challenge-tests were run until mortality naturally ceased. Time-until-event data were analyzed with a mixed cure survival model using Gibbs sampling, treating susceptibility and endurance as separate genetic traits.</p> <p>Results</p> <p>Overall mortality at the end of test was 28%, while 38% of the population was considered susceptible to the disease. The estimated underlying heritability was high for susceptibility (0.41 ± 0.07), but low for endurance (0.07 ± 0.03). Furthermore, endurance and susceptibility were distinct genetic traits (r_g= 0.22 ± 0.25). Estimated breeding values for endurance and susceptibility were only moderately correlated (0.50), while estimated breeding values from classical models for analysis of challenge-test survival (ignoring the cured fraction) were closely correlated with estimated breeding values for susceptibility, but less correlated with estimated breeding values for endurance.</p> <p>Conclusions</p> <p>For Taura syndrome resistance, endurance and susceptibility are apparently distinct genetic traits. However, genetic evaluation of susceptibility based on the cure model showed clear associations with standard genetic evaluations that ignore the cure fraction for these data. Using the current testing design, genetic variation in observed survival time and absolute survival at the end of test were most likely dominated by genetic variation in susceptibility. If the aim is to reduce susceptibility, earlier termination of the challenge-test or back-truncation of the follow-up period should be avoided, as this may shift focus of selection towards endurance rather than susceptibility.</p

Parámetros genéticos para crecimiento comercial, sobrevivencia y manchado en tilapia roja (oreochromis sp.) en colombia

El objetivo del presente trabajo fue estimar los efectos genéticos para peso al momento de sexaje, crecimiento y sobrevivencia hasta cosecha, y proporción de mancha (área de mancha y presencia/ausencia de mancha) durante la fase comercial en un grupo de 86 familias de hermanos enteros y 31 familias de hermanos medios de tilapia roja (tilapia sp).  La media de peso durante la fase de crecimiento comercial fue de 181,4 g  (184 g  para machos y 178 g para hembras), los machos significativamente más grandes que las hembras (P and lt; 0,001). Las variables de sobrevivencia, área de mancha y ausencia de mancha no presentaron diferencias entre los sexos. Las heredabilidades estimadas (h2±E.S) para crecimiento comercial y sobrevivencia fueron 0,23±0,02 y 0,05±0,03, respectivamente. El porcentaje de mancha y la ausencia y presencia de la misma mostraron heredabilidades cercanas a cero, lo cual indica que estos dos caracteres están relacionados más con efectos ambientales que con efectos genéticos aditivos. Se encontró una correlación favorable y significativa entre sobrevivencia y crecimiento comercial (0,24; P and lt; 0,05). Los resultados de este trabajo indican que mediante la explotación de la genética aditiva es posible mejorar el desempeño de los animales para crecimiento comercial y sobrevivencia en la tilapia roja, mientras que poco progreso se puede esperar por medio de la selección para variables relacionadas con el manchado corporal en la población evaluada

Learning the characteristics of engineering optimization problems with applications in automotive crash

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