Questionnaire


Reproduction

Hatching probability

If fairy tern eggs are brought from Australia to genetically rescue tara iti, do you expect the hatching probability of eggs laid from admixed pairs to be different from those laid by non ad-mixed tara iti pairs (0.6 ± 0.11 since 2010)? If so, what do you believe that value will be?




Expert Minimum Plausible Most Likely Maximum Plausible Confidence
FK 36.9 70.0 85 90
HK 67.0 75.0 83 100
IR 40.0 65.0 80 95
JZ 30.0 50.0 70 85
KB 50.0 70.0 80 75
NR 0.0 54.4 65 70
VK 30.0 80.0 100 85
XQ 20.0 70.0 80 100

Comments

Mixed offspring
  • VK: Given strong evidence of inbreeding depression, admixture should bring fitness benefits to the offspring by masking deleterious alleles by increased heterozygosity. Boosting immune genes should be beneficial too. Given the closest relative is a different species, there might also be some negative consequences of admixture, e.g. if genetic incompatibilities have evolved between species. Admixed individuals will get one copy of the genome from each parental species, so may not be affected too strongly. On balance, I feel the benefits of admixture may outweigh the costs, especially if there is evidence of historical gene flow between these species.
  • XQ: I expect an improvement in the hatching probability of hybrids because the high inbreeding in tara iti seems likely to be contributing to low hatching rate (so hybrids will be less inbred) - albeit I note that there are other less inbred bird species with lower hatching rates, so inbreeding is a contributor but not a confident predictor of low hatching success
  • HK: increase in egg hatch rate following genetic rescue reflects the stage’s high sensitivity to inbreeding depression and the strong empirical signal from comparable bird case studies. In small, isolated populations with high long runs of homozygosity, recessive deleterious alleles accumulate, leading to reduced fertility, increased embryo mortality, and lower hatch success. Outcrossing introduces new alleles, masking many of these lethal or sublethal variants and restoring normal embryonic development. Effect size given is consistent with other bird species where recovery is particularly strong at the earliest life stage, where genetic load is expressed most acutely. This stage can respond rapidly (within the first post-rescue breeding season) once donor genes enter the reproductive pool.
  • FK: I consider the hatching probability of eggs from admixed pairs is likely to be higher than the current hatching probability. In the information presented ~22% of eggs failed to hatch due to infertility or early embryo death - and I consider there could be an increase in hatching probability associated with reduction in this cause of failure of ~10% with alleviation of inbreeding. However, given my uncertainty around the changes, I have not increased the lowest plausible value, but I consider there to be a higher upper plausible value.


Fledging probability

If fairy tern eggs are brought from Australia to genetically rescue tara iti, do you expect the fledging probability of hatched eggs laid from admixed pairs to be different from those laid by non-admixed tara iti pairs (0.58 ± 0.05 since 2010)? If so, what do you believe that value will be?



Expert Minimum Plausible Most Likely Maximum Plausible Confidence
FK 47 65 85.0 90
HK 62 70 78.0 100
IR 40 58 75.0 98
JZ 0 25 50.0 80
KB 50 60 70.0 75
NR 0 66 70.0 70
VK 40 75 90.0 81
XQ 47 58 68.2 86

Comments

Mixed offspring
  • VK: Fledging probability in the wild will depend on environmental stochasticity, parental behavior (and parental quality as a parent) and balance between the contrasting effects of heterosis and outbreeding depression during admixture (i.e. quality and compatibility of the genomes). The former two factors could be managed to some degree through the breeding program, by reducing environmental stochasticity and threats.

  • HK: more modest than for hatching but still considerable gains. Fledging rate reflects both genetic and environmental influences. While early embryo mortality is driven largely by recessive lethal alleles, chick survival to fledging can also be affected by physiological robustness, immune function, and parental care quality, all of which may be compromised in inbred individuals.

    Introducing unrelated genetic material can improve chick condition through heterosis, enhancing growth rates, thermoregulation, and resistance to disease etc. The effect would manifest once admixed chicks begin to fledge and should persist with ongoing introductions that maintain genetic diversity.
  • XQ: I think fledging probability is predominantly environmentally driven. This presumes Australian fairy terns brought over as eggs are fully imprinted by their foster parents and provide the same level of care of offspring as tara iti parents do
  • FK: I consider the fledging probability of chicks from hatched eggs is likely to be slightly higher that the current fledging probability as the chicks may be less subject to disease. However, given my uncertainty around the changes, I have not increased the lowest plausible value, but I consider there is a higher upper plausible value.


Clutch size

If fairy tern eggs are brought from Australia to genetically rescue tara iti, do you expect the clutch size of a female born from admixed pairs to be different from that of non-admixed tara iti (1.71 ± 0.45 since 2010)? If so, what do you believe that value will be?



Expert Minimum Plausible Most Likely Maximum Plausible Confidence
FK 0.81 1.71 2.61 100
HK 1.75 1.80 1.85 100
IR 0.70 1.80 2.75 99
JZ 1.00 1.00 2.00 80
KB 1.00 2.00 3.00 75
NR 0.00 1.70 2.60 80
VK 0.50 2.00 3.00 95
XQ 0.81 1.71 2.61 95

Comments

Mixed offspring
  • VK: Expecting a slight positive shift towards higher value due to heterosis, while recognizing that outbreeding depression may (potentially temporarily) make this number lower. Without knowing the clutch size for the Australian fairy terns and tara iti before inbreeding, assuming that clutch size 2 is the norm and 1 and 3 are rarer.
  • FK: I don’t believe there will be a change in clutch size, as the information I have seen indicates that Australian fairy terns have a similar clutch size (i.e. clutch size does not appear to be affected by inbreeding/ROH)
  • XQ: I think clutch size is likely fairly similar between the two species and will have similar determinants i.e. some genetic variation but also resource allocation by the female according to her condition.
  • HK: genetic-rescue effect is likely to be smaller than for hatchability but could still be meaningful. Reduced clutch size in inbred females could result from lower body condition, disrupted endocrine function, or impaired allocation of resources to eggs etc. effects probably subtler than early embryo mortality. Introducing genetically diverse individuals could increase mean clutch size through improved female health and reproductive investment. Given that clutch size in terns is often constrained by evolutionary life-history strategy (1–2 eggs), any increase might manifest more in the proportion of females laying two eggs rather than a large shift in the mean. A conservative assumption would therefore be a small positive shift appearing after the first admixed females begin breeding.


Survival

Juvenile survival

If fairy tern eggs are brought from Australia to genetically rescue tara iti, do you expect juvenile survival from admixed pairs to be different from that of non-admixed tara iti pairs (0.69 ± 0.07 since 2010)? If so, what do you believe that value will be?



Expert Minimum Plausible Most Likely Maximum Plausible Confidence
FK 54.5 72.0 90.0 90
HK 70.0 75.0 80.0 100
IR 44.5 68.7 85.9 95
JZ 20.0 40.0 70.0 85
KB 60.0 75.0 85.0 75
NR 0.0 40.0 81.7 80
VK 40.0 85.0 100.0 95
XQ 54.5 75.0 82.9 88

Comments

Mixed offspring
  • VK: Juvenile survival will depends a lot on the level of inbreeding, as the chick must go through many developmental processes during its first year, many of which could be impaired by inbreeding, lowering overall fitness. Still, accepting a possibility that some genomic incompatibilities may strongly impact some process, and may strongly limit fitness of some individuals. Overall, expecting benefit of heterosis to outweigh outbreeding depression.
  • FK: I believe admixed juveniles are likely to experience slightly higher fitness, although not a substantial increase as they will still face numerous challenges associated with recent independence and dispersal. As with the other vital rates, I consider the lower plausible value remains unchanged but there is a chance there could be a reasonably large increase in the highest plausible value (to capture my uncertainty given the current lack of understanding of the extent to which juvenile survival is constrained by inbreeding depression).
  • HK: life stage that integrates multiple inbreeding-sensitive traits e.g., growth rate, immune competence, and foraging efficiency that influence survival through the critical post-fledging period. inbred juveniles may suffer reduced muscle mass, impaired thermoregulation, and heightened susceptibility to disease, all of which can translate into high first-year mortality. genetic rescue is expected to reduce the expression of deleterious recessives that compromise early survival. The effect would likely appear from the first generation of admixed juveniles and persist if periodic introductions maintain genetic diversity.
  • XQ: Again, I expect an improvement in the juvenile survival probability of hybrids because the high inbreeding in tara iti seems likely to be contributing to some loss of juveniles. Because hybrids will be less inbred, we might expect their survival to be higher.


Immature survival

If fairy tern eggs are brought from Australia to genetically rescue tara iti, do you expect immature survival from admixed pairs to be different from that of non-admixed tara iti pairs (0.92 ± 0.06 since 2010)? If so, what do you believe that value will be?



Expert Minimum Plausible Most Likely Maximum Plausible Confidence
FK 79.6 92.2 99.0 100
HK 90.0 93.0 96.0 100
IR 76.6 92.2 99.0 96
JZ 60.0 80.0 90.0 80
KB 85.0 95.0 98.0 100
NR 79.7 88.0 96.2 100
VK 79.6 95.0 100.0 100
XQ 79.6 92.2 99.0 100

Comments

Mixed offspring
  • HK: probably only show modest gains from genetic rescue. By this stage, many strongly deleterious recessives that drive early mortality have already been “filtered out” in the egg–chick–juvenile stages. baseline immature survival is already high, so probably a ceiling effect (less room for improvement). Any gains would come from heterosis in sub-lethal traits (better body condition, immune function etc).
  • FK: Immature survival probability is already high (most likely value) and the current upper plausible value captures what I consider would be the upper plausible value with admixture.
  • VK: Not expecting a strong effect here, but still some overall positive effect of admixture (based on empirical examples from other systems)
  • XQ: This value is already very high for tara iti. It suggests that individuals who have made it this far are not carrying a strong deleterious inbreeding load - those individuals may have been lost at previous life stages. This survival rate is likely in the majority environmentally driven, and so would not differ between hybrid and non-admixed offspring


Adult survival

If fairy tern eggs are brought from Australia to genetically rescue tara iti, do you expect adult survival from admixed pairs to be different from that of non-admixed tara iti pairs (0.9 ± 0.03 since 2010)? If so, what do you believe that value will be?



The same plot but truncated to survival >70%


Expert Minimum Plausible Most Likely Maximum Plausible Confidence
FK 84.3 92.0 98.0 100
HK 90.0 92.0 94.0 100
IR 74.3 89.5 94.7 95
JZ 70.0 85.0 90.0 80
KB 88.0 92.0 95.0 75
NR 0.0 89.7 92.8 80
VK 84.3 95.0 99.0 95
XQ 84.3 85.0 94.7 88

Comments

Mixed offspring
  • VK: Expecting shift due to heterosis, improvement of immune system and masking deleterious variation that may have lowered fitenss
  • FK: Based on analyses I have undertaken for other species, I consider there could be a slight increase in adult survival in admixed birds. This is reflected in both the most likely value and the highest plausible value. I have left the lowest plausible value unchanged, as I also consider it feasible that there will be no increase compared to survival rates in the existing population.

  • HK: probably the least responsive life stage to genetic rescue in long-lived species. By the time individuals reach adulthood, they have already passed multiple survival filters, so those carrying severe inbreeding-related defects are less likely to be present in the breeding population.

    That said, high inbreeding can still depress adult survival through reduced physiological resilience, impaired immune function, and lower tolerance to environmental stressors (e.g., food shortages etc). Outcrossing can mitigate these effects by increasing heterozygosity, which may improve overall health, stress recovery, body condition etc. For tara iti, there is a high starting baseline and limited scope for improvement, but even small gains would have significant impact on long-term population persistence .
  • XQ: As with my previous answer, I believe adult survival is mostly environmentally rather than genetically driven. Having said that, there may be some innate behavioural differences between the Australian fairy tern and tara iti that mean the Australian fairy tern don’t make the ‘best’ decisions for their survival. So, there may be a slightly lower survival rate of these hybrid adults carrying genetics from both subspecies.