Can zoos improve breeding success by allowing animals to choose their partner?

4 days ago
4 min read

Written by Tom Roth, Utrecht University, The Netherlands

Link to the paper: https://doi.org/10.1163/1568539X-bja10346

Conservation breeding programmes match animals in zoos with the goal of keeping populations genetically healthy. But, those planned matches often fail in practice when animals are not interested in their ‘match’. One potential solution to this problem is allowing animals to choose their own partners, as this has been shown to increase reproductive success. However, because animals are often housed in different locations, testing such partner preferences comes with important challenges.

When the perfect match fails

On the TV show Married at First Sight, candidates marry a partner they have never met before. Experts decide who would be their best match and the couples are then expected to make their match work. Viewers know that this approach is rather unsuccessful: a match may look promising on paper, but that does not mean people will actually feel attracted to each other.

Interestingly, many zoo-housed animals are paired in a similar way. Zoo breeding programmes aim to sustain healthy populations by avoiding inbreeding and maintaining genetic diversity. To do this, they recommend which animals should be paired and whether animals should be transferred between zoos. However, studies have shown that successful breeding often does not happen, partly due to pair incompatibility.

This is problematic for two reasons:

First, being paired with an unpreferred partner can affect the welfare of animals. Surprisingly little research has been done on this topic, but one study found that Gouldian finches had higher levels of corticosterone, a hormone associated with stress, when they were paired with an incompatible partner.
Second, if recommended pairs fail to reproduce, this can affect the health of the zoo population. It may lead to smaller populations or a loss of genetic diversity.

Why animal preference matters

One possible solution is to take the preferences of animals into account. Many studies have shown that animals more often reproduce successfully when paired with a preferred partner. This has been found in very different species, ranging from monogamous birds to promiscuous fruit flies. But how do researchers test an animal’s preferences?

Most studies use a version of the “lover’s lane” design, where one animal can interact with multiple potential at the same time, but without being able to mate. Researchers observe how much time the animal spends near each potential partner, or how it behaves towards them. The animal is then paired with either a preferred or non-preferred partner, making it possible to test whether partner preferences affect reproductive success.

This approach has been very useful for showing that partner choice matters. However, it is difficult to apply in zoo populations, where animals are often spread across different institutions, sometimes in different countries. Bringing individuals together just to test who prefers whom would be expensive and potentially stressful. So, if zoos want to include partner preferences into their breeding programmes, they need a different approach.

Can animals choose from a distance?

One possibility is to test animal preferences from a distance by presenting them with pieces of information from potential partners. Depending on the species, this could include pictures, sounds, smells or a combination. This approach has not been widely tested yet, but studies suggest it might have potential. One study with cheetahs presented females with urine samples from different males. Females spent more time sniffing urine samples of males that were genetically different from them, suggesting a preference for these males. In my own research, I studied whether orangutans showed visual preferences for certain males. Male orangutans can look very different: while some individuals have large cheek pads and other masculine traits, others do not. We tested whether orangutans looked more at masculine males, and whether they showed preferences for pictures of specific individuals. While visual traits indeed guided attention, clear preferences for specific individuals were absent.

Importantly, both of the studies mentioned above did not test whether individual responses predicted breeding success. A recent study with common voles did investigate this. Females were allowed to explore scent samples of two males, and researchers quantified which scent they showed more interested in. Some females were then paired with the male whose scent they preferred, while others were paired with a non-preferred male. Females paired with a preferred male produced more offspring, suggesting that responses to a single information source, like scent, can inform us about an animal’s partner preferences.

In summary

The findings of existing research suggest that long-distance preference testing has potential for conservation breeding. However, more research is needed before these methods can be widely applied. It remains unclear how well responses to pictures, sounds, or smells predict breeding success. Importantly, genetic management will remain essential as well: zoos need to avoid inbreeding and maintain genetic diversity. Nevertheless, partner preference testing could become an additional tool. It may help zoos to form pairs that are not only genetically valuable, but also likely to reproduce. After all, whether in reality television or conservation breeding, a match that looks good on paper might not work in real life.

Written by Tom Roth, Utrecht University, The Netherlands

Link to the paper: https://doi.org/10.1163/1568539X-bja10346