Question

One of the potential problems with supplementing endangered wild populations with captive bred individuals is that captive bred organisms often have reduced fitness compared to their wild counterparts. Reasons for this are varied, but work suggests it is a combination of reduced genetic variation in captive bred populations (small population sizes and assortative mating leading to reduced genetic variation) as well as reduced fitness due to individuals adapting to a captive environment as opposed to a wild environment. Fundy Atlantic salmon (Salmo salar) are an endangered salmon species whose numbers have declined to a point that scientists started to supplement their wild numbers with captive bred individuals. The question you will answer here is: is supplementing wild salmon populations with captive-bred individuals beneficial if the captive bred individuals have lower fitness than the wild population?

The average number of eggs laid by females in the wild population is about 2,500/female. The captive bred individuals typically exhibit about 30% lower fecundity than wild individuals (some estimates are up to 40% lower, but we will use 30% for purposes of this assignment).

1. If the heritability of fecundity is 0.1, what do you predict the fecundity of the new population will be (assume you add just as many new individuals as were already in the wild population)? (2 points)

2. Now consider if the heritability of fecundity was higher, let’s say 0.3 Now what do you predict the fecundity of the new population will be (using all the original numbers, not after one generation of selection)? (2 points)

3. If fecundity exhibits high heritability, what do you predict will happen to population numbers in this population over time if captive bred individuals are added every year (2 point)?

Answer 1

Captive bred populations should be kept in a captive mode and I feel strongly that the overall genetic variability of wild type and their fecundity will go down if captives are introduced into the population. Captive species may enounter certain diseases which can also be transmitted to the wild type, thus reducing their fecundity and overall survival.The cumulative effect of captive introduction to wild may lead to lesser variation amongst the entire population. The population will definitely improve although the ability to fight diseases may go down. But with proper intervention one can save the species.One needs to optimise the number of captives that need to be introduced into wild based on some pilot experiments, if that is so important.

1. Number of eggs of wild type= 2500

Number of eggs of captive=(70/100)*2500=1750

Total number of atlantic salmons= 2500 (wild)+2500 (captive)

Thus new production upon mating= (2500+2500)*0.1*0.7=350

Thus new population due to genetic variation reduction would have 2500-350=2150 salmons.

On the other hand, population would be 5000*0.3*0.7=1050. Thus new population=2500-350+1050=3200 out of population of 5000 individuals.

3. It means that the population will definitely surge as heritability of fecundity is high. Also, there might be an improved genetic variation, initially more compared to captive but less than wild type but with time, the variation will go down but population will definitely surge.