Yeah love is indeed a mysterious thing and has always captured our imaginations. One of the most famous tragic love stories was the Romeo and Juliet by William Shakespeare. Tragic in the sense that the main protagonists die at the altar of their own love. So, what makes love so special? Or indeed as a biologist i ask what is the need for love. Just look what goes into the love process. Endless dating games, elaborate preparations, endless flirtations, also many humiliations and finally if you are lucky the one acceptance.
But wouldn’t it be simpler to just think about procreation alone, i.e., reproduce for the sake of propagation?? Since, evolutionary struggles dictate that there exists differential reproduction and hence propagation of one’s own genes is the thing which ultimately matters. So, then why do we go for this protracted cycle?
To answer this question albeit in an indirect way authors – Malika Ihle, Bart Kempenaers and Wolfgang Forstmeier all from Department of Behavioral Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, Seewiesen, Germany conducted a remarkable experiment. The results of this experiment was published recently in PloS Biology – Fitness Benefits of Mate Choice for Compatibility in a Socially Monogamous Species.
As we know that to actually conduct a cost/benefit analysis of love is easier said than done and there would be innumerable ethical concerns regarding the bounds of experimentation with humans. This present study however, used a model animal in an elegant experiment which was designed to find the reproductive consequences of mate choice.
The model species used here was the –zebra finch (Taeniopygia guttata, a native bird of Australia).
They started off with a population of 160 birds that had recently been isolated from the wild, and then set them up on a sort of speed-dating session, with groups of 20 females to choose freely between 20 males (See figure 1 below). Once the birds had paired off, half of the couples (the “chosen” or C group) were allowed to live happily ever after. For the other half, however, the authors intervened like overbearing Indian parents, and split up the happy pair to forcibly pair them up with other broken-hearted individuals (the “non-chosen” or NC group). The bird couples of both C and NC groups were then left in aviaries to breed. The authors then measured the couple’s behaviour and the number and paternity of dead embryos, dead chicks and surviving offspring.
The first batch of results is elegantly shown in the figure above.The overall reproductive fitness (measured as the final number of surviving chicks) was 37% higher for individuals in chosen pairs than those in non-chosen pairs. But since reproductive fitness is the sum total of different effects which add up to the total number of offspring produced, it’s vital to look at those parameters and understand the mate choice in C group affected the fitness. To start off the authors noted that both the C and NC group laid similar number of eggs which suggests that their initial investment towards egg laying is not affected by the group they are in and also oblivious to the mismatched mate picked up by the authors. But the nests of NC group had almost three times as many unfertilized eggs as the chosen ones, and a greater number of eggs that were neglected (either buried or lost).
The authors in their earlier studies had known this fact that embryo deaths happened mainly due to genetic incompatibility between the parents, however the egg hatching related deaths happened due to behavioural incompatibility. So, the next step was to compare these two phenomena in the two C and NC groups. They found that though the embryo mortality was similar in both the groups, however mortality of the hatched chicks was comparatively
higher in the NC couples. This suggests that its the behavioral incompatibility
between the non-chosen (NC) parents, and not genetic incompatibility which might be the driving factor behind the observed reduction in overall fitness (Fig. 3, below).
The authors in the end ascribe this difference in reproductive fitness to the behavioural incompatibility between the two groups. They also mention – ‘‘The mechanisms behind such behavioural compatibility, in terms of willingness or ability to cooperate with certain individuals and in terms of coordination between partners need further study, in particular in the context of offspring provisioning.”
In humans, some studies suggest that individuals are more satisfied, more committed, and less likely to engage in domestic violence, when involved in a love-based rather than an arranged marriage (2,3,4). The challenge there is also to find out whether stable and happy marriages result from motivation to cooperate (and to identify what stimulates such feelings, see 5-8), or from congruence in terms of partners’ intrinsic behavioural types .
- Ihle M, Kempenaers B, Forstmeier W. Fitness Benefits of Mate Choice for Compatibility in a Socially Monogamous Species. PLoS Biol. 2015; 13(9): e1002248. doi:10.1371/journal.pbio.1002248
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