Dunnock and Alpine Accentor Mating Systems Flashcards
Conflict over Care
Detailed studies of single species provide valuable insights into the evolution of mating systems, particularly when they exhibit variation in their mating system. Two intensively studied species are the dunnock Prunella modularis and alpine accentor Prunella collaris, congeners in the family Prunellidae.
Dunnocks exhibit polygyny, polyandry, monogamy, and polygynandry, while alpine accentors are always polygynandrous. In both species, all individuals within each system are unrelated. Studies of these species illustrate many of the main themes that you have heard about in other lectures on conflict over care and mating systems.
Ecological basis for mating systems
The variation in mating systems observed within and between species is related to the distribution of resources in the environment. This determines female ranges, which in turn determine male ranges.
Dunnocks
Females defend exclusive territories against other females. The emergent mating system depends on the ability of males to monopolise territories, i.e. female territories are the template for male distribution. Females in polygyny/monogamy have small territories (mean = 2,500 m2) defendable by one male, while polyandrous females have larger territories (5,500m2) where a single male (= alpha male) is unable to prevent a second male (= beta male) from settling. Experimental provisioning of territories showed that female territory size was influenced by food availability, while male distribution was unaffected. ‘Fed’ females were less likely to be polyandrous than ‘unfed’ females (Davies & Lundberg 1984 - J Anim Ecol 53: 895-912).
Alpine accentors
Females have relatively enormous overlapping ranges (11 ha per female). These large ranges are necessary to exploit the spatially and temporally patchy invertebrate prey blown up from the valleys. At lower altitudes (where dunnocks live), food is more abundant and predictable. Because of their range size, individual males are unable to defend single females, so two to four males share a large undefended range (18 ha) encompassing the ranges of two to four females, hence polygynandry is the norm in this species (Davies et al. 1995 - Anim Behav 49: 769-788).
Paternity and parental care
In both species, males compete with each other in order to maximise their mating success, and then subsequently provide parental care in relation to their paternity.
Dunnocks
Dunnocks have a very high copulation rate (c.2 cop’s/hour for 7-10 days), preceded by an extraordinary cloaca-pecking display (Davies 1983 - Nature 302: 334-336; Hatchwell & Davies 1992 - Anim Behav 43: 595-609). The pattern of matings and paternal care varies among mating systems.
Monogamy - Male monopolises matings, gaining 100% paternity. Male provides c.50% of nestling care.
Polygyny - Male monopolises matings, gaining 100% paternity. On average, females get less male help with feeding nestlings: male may feed only one brood, leaving the second female to care for her brood alone, or may feed both broods part-time.
Polyandry – With two males on a territory, there is intense competition among males for matings. Alpha male may gain all matings but beta male often obtains some (up to 50%), so paternity may be shared. Paternal care is related to paternity share, estimated from their share of copulations (Burke et al 1989 - Nature 338: 249-251; Davies et al. 1992 - Anim Behav 43: 729-745).
Alpine accentors
As in dunnocks, there is intense mating competition among males, and an even higher copulation rate (c.3 cop’s/h with c.2 inseminations/cop). Paternity is often shared among males (up to three fathers/brood), and paternal care is again related to mating share, and hence paternity (Hartley et al. 1995 - Anim Behav 49: 789-903).
Competition among females
In both species, females attempt to maximise the amount of male assistance they get with parental care by frequent solicitation of copulations.
Dunnocks
In polygyny and polygynandry, females are aggressive towards, and often fight with other females to restrict competition for a male’s parental care. Furthermore, polyandrous females actively evade alpha male guarding behaviour and encourage beta males to copulate with them. If successful, both males subsequently help to feed her brood (Davies 1985 - Anim Behav 33: 628-648; Hatchwell & Davies 1990 - Behav Ecol Sociobiol 27: 199-209).
Alpine accentors
Females compete among each other for paternal care by increasing their solicitation rate if other females are fertile and by advertising their fertility by (i) revealing their bright red cloaca, and (ii) singing to attract males (Davies et al 1996 Anim Behav 51: 27-47; Langmore et al 1996 Proc R Soc, Lond B 263: 141-146).
Reproductive success and sexual conflict in accentors
All of these behaviours make good sense if we consider the effect of male care on nestlings and hence on the reproductive success of males and females in different systems. Ultimately, this results in sexual conflict over the preferred mating system (Davies 1985 - Anim Behav 33: 628-648).
Dunnocks
The success of a brood is largely determined by the amount of male care, i.e. with more paternal care, the lower the level of starvation, and the larger the number of young produced (Davies & Hatchwell 1992 - J Anim Ecol 61: 259-272).
Thus females do worst in polygyny where they No. young per season
have to share a male with another female, and
they do best in polyandry where both males help
to feed her brood. Intermediate success is achieved
in monogamy. By contrast, males do best in
polygyny because although each female has lower
success, together they produce more young then in
monogamy. Males do worst of all in polyandrous
systems where females copulate with both males
because although more young are produced,
paternity is shared between the two males.
Alpine accentors
There is no effect of the amount of male care on the number of young produced by a female, but the mean weight of chicks increases as male help increases. This may be important for subsequent survival of young (Davies et al 1995 - Anim Behav 49: 769-788).
Conclusion
Ecological factors set the scene for the evolution of accentor mating systems. In both species, mating systems are characterised by sexual conflict, with each sex exhibiting adaptations designed to maximise their own reproductive success at the expense of others.
