[MARMAM] New publication: Mating Group Size in Dusky Dolphins (Lagenorhynchus obscurus)

Dara Orbach dnorbach at gmail.com
Wed Jun 11 14:50:52 PDT 2014


Dear Colleagues,

We are pleased to announce the publication of the following article in
Ethology.

Orbach, D. N., Packard, J. M., Würsig, B. (2014), Mating Group Size in
Dusky Dolphins (Lagenorhynchus obscurus): Costs and Benefits of Scramble
Competition. Ethology. doi: 10.1111/eth.12253

Abstract: In fission–fusion social systems with scramble competition
between males, multiple males join mating groups while surrounding an
oestrous female. If male decisions to join a mating group have been shaped
by natural selection, then there should be an optimal group size resulting
from the trade-offs between the benefits of monopolizing a female in small
groups and the energy lost in defending her from rivals in large groups.
Male dusky dolphins (Lagenorhynchus obscurus) off Kaikoura, New Zealand,
provide a unique opportunity to assess the optimum mating group size
because they join transient mating groups not confounded by foraging or
predator evasion. Within aggregations of up to 1000 individuals, males
search for oestrous females, encountering choices of staying with a large
mating group or leaving to find a smaller group. Mating groups typically
involve multiple males mating with a single female. We conducted focal
follows of mating groups (N = 44) by vessel from November 2011 through
January 2012. We used video and a GPS to record group size, behaviour and
movement. For each group, we measured potential costs (Swim Speed, Loss of
Monopolization Potential) and benefits (Copulation Rate and Duration,
Energy Savings). Only Loss of Monopolization Potential was positively
correlated with group size, while Energy Savings was negatively correlated.
Using these two factors as utility functions, we constructed an optimality
model and predicted the optimal mating group size to be seven individuals
with a range of 4–11 individuals due to variance. The observed modal mating
group size was five dolphins, with a range of 2–15. We compare variation in
mating group currencies and sizes to past studies. We discuss potential
limitations of applying optimality models to predict mating group size for
socially complex and behaviourally plastic species such as dolphins.

This article is available online (
http://onlinelibrary.wiley.com/doi/10.1111/eth.12253/full) or by e-mail
request (dnorbach at gmail.com).


Cheers,
Dara Orbach


Ph.D. candidate
Marine Mammal Behavioral Ecology Group
Department of Marine Biology- IDP
Texas A&M University at Galveston
dnorbach at gmail.com
http://www.tamug.edu/mmbeg
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