Sunday, March 8, 2009

Sexual Competition and Lemurs

Ivan Norscia, Daniela Antonacci and Elisabetta Palagi recently published an article in which inter- and intrasexual competition between wild prosimians is examined from the perspective of economic power distributions and as a metaphor for financial markets.

[Lemur, Propithecus verreauxi]

Essentially, their findings indicate that competition for females by males typically manifests as an “olfactory tournament” in which males try to “out bid” rivals by more proactively scent marking. This strategy accurately reflects dominance between males and is less costly than engaging in combative or otherwise aggressive behaviors.

Intersexual competition (male-female selection) in the lemur is accomplished via a strategy of “commodity exchange” in which males offering the best resources (food) or services (grooming) are preferred and ultimately gain advantage through more frequent copulations.

The article (available here) is clearly written and is jargon free; it could have just as easily appeared in a Pop-Sci magazine as a journal. For this reason, as well as to compliment my prior posts discussing sexual selection, I’ve pasted the Introduction and Videos below.

NOTE- I removed references for ease of reading; please refer to the original article linked above for corroboration.

"In biology, as well as in economics and politics, power is a key concept for understanding asymmetrical dyadic relationships. Distributive power can originate from both dominance (when force is used) and leverage (when the use of force is not possible). An individual has leverage over another when that individual possesses something that the other needs but cannot acquire through coercion. In this case, trading becomes essential for mutually beneficial interactions within social groups, both in economical and biological markets. An important feature of market models is that the expected future gains are actively influenced by playing off potential partners against each other. The typical game theory approach includes only two players and, although this is changing within economics as well as biology, the classical models do not take into account partner choice. In contrast, the biological market theory includes multi-player models, that is theoretical games with at least three or more “players” (traders, in the market systems). Two or more classes of traders (sex classes, rank classes, etc.) exchange commodities in biological markets to their mutual benefit. Different group members can offer different kinds of commodities in exchange for alternative ones that they do not currently possess. Usually, competition acts as the driving force within the same trader class (including all members offering the same kind of commodity) while cooperation can occur between different trader classes.


Male countermarking behaviour on a female scent deposition

In the mating market, the balance of power tilts in favour of females whenever males cannot force females into mating (as it happens in sexually monomorphic species or when females form coalitions). Consequently, males depend on females for breeding opportunities and must compete to prove their superiority to females, thus increasing their possibility to be selected. Males can engage in both contest competition via physical/ritualized fighting and outbidding competition, in which a male plays off rivals by making a better offer. In the latter case, males can secure the favours of a female by advertising their quality (e.g. the dominance status) through visual or olfactory displays and/or by being more generous than others in providing a commodity in exchange for female access (competitive altruism). One of the most valuable commodity that can be offered in social mammal groups is grooming, which is used for parasite removal, stress reduction, and as social cement to start, consolidate, or repair relationships. Grooming is a commodity that can be exchanged for itself or for breeding opportunities.


Copulation followed by a grooming session

Sociality is widespread among mammals and particularly among anthropoid primates (monkeys and apes). In prosimians (the most ancestral group of primates) sociality is the exception more than the rule. Among Malagasy prosimians (lemurs), few species combine a powerful olfactory system (retained from basal mammals) and puzzling features like group living, female priority over resources, and absence of sexual dimorphism. Such combination of features makes gregarious lemurs the ideal model to understand the biological bases of mate selection by females, who cannot be accessed by force or using food as exchange commodity. In particular, we selected the diurnal species Propithecus verreauxi of south/southwest Madagascar to find out which male strategies are successful to maximize breeding opportunities."


Copulation in which intromission and thrusting were unambiguously observed

Ivan Norscia, Daniela Antonacci, Elisabetta Palagi (2009). Mating First, Mating More: Biological Market Fluctuation in a Wild Prosimian PLoS ONE, 4 (3) DOI: 10.1371/journal.pone.0004679

1 comment:

  1. Daniela AntonacciMay 6, 2010 at 8:40 AM

    Dear Johnny,
    Thanks a lot for your positive feedback on our article. We are still working on sifaka's behaviour, finding out more and more surpises...We will let you know on forthcoming publications if you want.

    Congratulation for your blog!