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Short and long-term consequences of the early environment

Periodic Reporting for period 1 - EARLYSTART (Short and long-term consequences of the early environment)

Reporting period: 2015-10-01 to 2017-09-30

It is well known that disturbances experienced in childhood have a strong impact on the life of an individual, with consequences in adulthood. The potential consequences of adverse early conditions will depend on the type of disturbance, the duration of the disturbance and the moment of development when the disturbance occurs, as there are more sensitive time windows in development than others. In the worse case scenario, it could lead to dysfunctional adults. There are many ways to buffer disturbances. One of them is social support, which in many instances comes from relatives. However, the family can also be the source of the disorder, for instance when an individual is raised in a dysfunctional family.
To address this question I have used the spotless starling, a common passerine bird in Spain. In passerine birds, the social system seems very stable. It consists of a monogamous pair that shares the care of the offspring. However, social pairs and genetic pairs usually differ. Both males and females can be promiscuous, and in a relatively high proportion of nests, some of the offspring are not genetically related to both social parents. Promiscuity is related to some personality traits: promiscuous females are more exploratory, more active, and thus, less nest-attending. Moreover, males paired with promiscuous females decrease their paternal share. In the same line, males can mate with more than one female at a time, and part nest attendance between them. Therefore, a female mated with a polygynous male (a male that defends more than one nest and more than one clutch), receives a lower share of paternal nest attendance. Nest attendance is essential for the good development of the offspring, and thus, offspring from a promiscuous parent might see their development compromised. In this project, I have investigated the link between personality, promiscuity and the effects on offspring development. I wanted to know how the early environment provided by the parents explained the life trajectories of their offspring. In particular, I wanted to know to what extent female personality affected the early environment experienced by the nestlings, whether males mated with promiscuous females reduced their parental care, and what were the consequences for the female and the offspring both in the short and in the long-term.
Dysfunctional families are a major issue in human societies. The results attained might help understand the long-term effects of being raised in such environments. Moreover, in a global change scenario, disturbances are expected, and to identify what are the consequences for the individual, as well as for the species might increase the awareness of protection measures.
To attain my goals, I have followed the fate of 225 breeding events of starlings nesting in nest boxes. They produced a total of 1112 eggs, from which 925 nestlings hatched.
In March, before starlings start laying eggs, we trapped the adults in their nest boxes. Trapping has several purposes. On the one hand, it serves to get important information about the condition of the animals. We weigh them, we measure them, and we individually mark them with leg rings. Moreover, we insert a small transponder, which will be very useful to track the individual throughout its life. In addition, trapping provides information about potential social pairs. Stable pairs sleep together in the nest box before reproduction begins, and thus, those animals trapped together in the nest box, have spent the night together, and are good candidates to breed together. An additional source of information that trapping provides is that we can assess the personality of the birds. Animals differ in the way they react to being handled; some scream, some struggle, and some are aggressive towards the observer, whereas others stay apparently calm. Those reactions are repeatable, which means that birds that attack in one trapping event, do attack too when trapped again. Those behaviours that are repeatable across time and contexts conform what we call the personality of the individual.
In April starlings synchronously start laying eggs. By daily checking the nest boxes we can assess the onset of egg laying, the number of eggs each pair lays, and the number of nestlings that hatch from those eggs. Nestlings are individually marked, so we can follow the fate of each individual. By doing so, we can know who are the nestlings that survive and the body condition they attain before fledging. From each nestling, we take a blood sample, which is later analysed in the genetic laboratory. From all those blood samples we can know the genetic father and mother, which sometimes differ from the mother and father that they had at the nest. This is very laborious, but the results are sometimes very surprising.
We found that female personality affected reproductive success. More explorative females were less successful, they raised less nestlings and less fledglings than less explorative ones. In addition, neophobic individuals, those that react strongly to novelty, started reproducing later in the season, with the concomitant risk of having less food available to feed the young. We could show that parents had a strong impact on the development of their young. Young development was affected by the time of the year they were born (starlings lay two broods in a year, one in April and a second one in May-June), the body condition of the mother, the number of siblings, and the promiscuity of the mother. We found that males attended the nest less than females, and that females paired with a male that attended less than average, compensated by increasing their own share. However, the compensation was partial, and low paternal care was translated into higher chick mortality. Compensation, in any case, is costly, and it can compromise the future reproduction of the female. We explored the costs of reproduction for females, and we found that high-quality females could heavily invest in one brood at apparently no cost. However, when extra-costs were added, in terms of enlarged broods (some females do not defend a nest and lay their eggs in others nests, what is called brood parasitism), they paid the cost later in life, by reducing the investment in future reproduction.
With this project, we expect to disentangle the long-lasting effects of different aspects of the early environment. So far, we have shown how parental personality affects reproductive success, how the social system modulates reproductive decisions, such as how much to invest in one breeding season, and the consequences on offspring development. All these results highlight the importance of studying the early social environment, as the adult phenotype is shaped by the experiences earlier in life.
A typical clutch of spotless starlings
The trapping crew
Nestlings
female (left) and male (right) spotless starling