Parallel Evolution of Bower-Building Behavior in Two Groups of Bowerbirds Suggested by Phylogenomics

The bowerbirds in New Guinea and Australia include species that build the largest and perhaps most elaborately decorated constructions outside of humans. The males use these courtship bowers, along with their displays, to attract females. In these species, the mating system is polygynous and the females alone incubate and feed the nestlings. The bowerbirds also include 10 species of the socially monogamous catbirds in which the male participates in most aspects of raising the young. How the bower-building behavior evolved has remained poorly understood, as no comprehensive phylogeny exists for the family. It has been assumed that the monogamous catbird clade is sister to all polygynous species. We here test this hypothesis using a newly developed pipeline for obtaining homologous alignments of thousands of exonic and intronic regions from genomic data to build a phylogeny. Our well-supported species tree shows that the polygynous, bower-building species are not monophyletic. The result suggests either that bower-building behavior is an ancestral condition in the family that was secondarily lost in the catbirds, or that it has arisen in parallel in two lineages of bowerbirds. We favor the latter hypothesis based on an ancestral character reconstruction showing that polygyny but not bower-building is ancestral in bowerbirds, and on the observation that Scenopoeetes dentirostris, the sister species to one of the bower-building clades, does not build a proper bower but constructs a court for male display. This species is also sexually monomorphic in plumage despite having a polygynous mating system. We argue that the relatively stable tropical and subtropical forest environment in combination with low predator pressure and rich food access (mostly fruit) facilitated the evolution of these unique life-history traits. [Adaptive radiation; bowerbirds; mating system, sexual selection; whole genome sequencing.]

A Darwinian Selection Based Explanation of Peacock’s Tail

There is no satisfactory explanation for why peacock possesses a tail, presence and especially courtship display of which makes the organism vulnerable to predation. Here, I present a model according to which in a polygynous mating system a mechanism which increases vulnerability to predation, a Zahavian handicap, evolves when other two mechanisms to identify high-quality males are either absent or are not sufficiently strong. The two mechanisms are: 1) male resource acquisition ability, and 2) male-male competition for females. The three mechanisms are not necessarily mutually exclusive. Assuming the locus for the tail and choosiness to be sex-specific, it is shown through stochastic simulation that sexual selection, mediated by the tail (a Zahavian handicap), leads to higher rate of increase in the quality of the population of tailed peacocks and tailed-choosy peahens (which exclusively mate with tailed peacocks) as compared to the population of tailless peacocks and tailless-choosy peahens (which exclusively mate with tailless peacocks), through a positive feedback, as daughters of tailed-choosy peahens are of higher average quality and, by virtue of not carrying the tail’s handicap, also fitness than daughters of tailless-choosy peahens. Also, the fold-change in the population of tailed peacocks and tailless-choosy peahens are higher than the fold-change in the population of tailless peacocks and tailless-choosy peahens, for all combinations of the initial conditions. The same results were got, though in milder form, when tailless-choosy peahens were replaced by undiscriminating peahens (which mate with tailless and tailed peacocks in proportion to their frequencies in the population). Although sons of tailed-choosy peahens have lower average fitness than sons of undiscriminating peahens, this difference is inconsequential, because in a polygynous mating system a single male can potentially mate with every female. The work presented here reconciles Zahavi’s handicap principle with Darwin’s theories of natural and sexual selection. Further, it is hypothesized that a genotype responsible for producing in males a reliable indicator of high quality (a Zahavian handicap) or paternal care ability generates mating desirability in females towards males possessing the indicator. It is demonstrated through simulation that this cross-gender pleiotropy expedites the evolution of tailed peacocks and tailed-choosy peahens and leads to higher rate of increase in their quality.

Bioacoustic cues and their relations to dominance rank in Père David’s deer stags

The vocal display of male animals during the breeding season has received particular attention. To find out whether male acoustic signals could be a quality-assessment cue of callers, we conducted a study on Père David’s deer (Elaphurus davidianus) characterised by a polygynous mating system and high male–male competition during the rutting season. We investigated the relationship between the stag’s acoustic properties and the dominance rank as an indication of quality. Results showed that (1) there were two types of calls, the common roar and the chasing bark, (2) there was no significant difference between the call duration of the common roar and the chasing bark among different dominance ranks, (3) in the common roar, the value of the fundamental frequency, formant frequencies and formant spacing decreased significantly with the rise of dominance ranks and (4) vocal intensity of the common roar differed significantly among the three dominance ranks such as the harem master, the challengers and the bachelors. Our results suggested that some acoustic features, such as formant frequencies, formant spacing and vocal intensity of the common roar were closely related to the dominance rank and could be effective indicators of male competitive ability.

Genetic evidence for multiple paternity in the critically endangered Cuban crocodile (Crocodylus rhombifer)

Conservation strategies can be most effective when factors influencing the persistence of populations are well-understood, including aspects of reproductive biology such as mating system. Crocodylians have been traditionally associated with a polygynous mating system, with genetic studies revealing multiple paternity of clutches in several species. The endemic Cuban crocodile,Crocodylus rhombifer, is currently listed as Critically Endangered, and is one of the least understood crocodylian species in terms of its mating behavior. Here, we tested a hypothesis of multiple paternity in the Cuban crocodile by collecting genotypic data at nine microsatellite loci for 102 hatchlings from five nests sampled at the Zapata Swamp captive breeding facility and analyzing them in relation to data previously collected for 137 putative parents. All five nests showed evidence of multiple paternity based on the numbers of alleles per locus, with sibship analyses reconstructing all nests as having four to six full-sib family groups. Accordingly, mean pairwise relatedness values per nest ranged from 0.21 to 0.39, largely intermediate between theoretical expected values for half-siblings (0.25) and full-siblings (0.50). It is not possible to differentiate whether the multiple paternity of a nest was due to multiple matings during the same breeding season, or a result of sperm storage. Our results reveal that theC. rhombifermating system is likely best characterized as promiscuous and suggest that the standard practice of enforcing a 1:2 sex ratio at the captive breeding facility should be altered in order to better maintain a demographically and genetically healthy ex situ population.

Black Bass Diversity: Multidisciplinary Science for Conservation

<em>Abstract</em>.—Attempts to infer mating systems in wild fish populations can be limited by the logistics of locating nests and thoroughly sampling offspring and potential participants. Captive populations are more easily evaluated but may exhibit modified behavior. We used microsatellites (17 loci) to determine parentage among production offspring and infer the mating system of raceway spawning Guadalupe Bass <em>Micropterus treculii</em>, which are part of a supplemental stocking program. Offspring were collected over the course of two production seasons (<em>n </em>= 303 and 492). Spawning activity was nonrandom, with respect to location and time in most compartments, and individuals that spawned were significantly larger, by length and weight, than individuals that did not. During the first year of captivity, significantly fewer males (21 of 60) than females (49 of 61) spawned. Inequalities between the number of nest locations used and the numbers of spawning males and females suggest that males recruited females to spawning sites. While most spawning females (61%) participated with a single mate, most spawning males (90%) participated with multiple females and only 3% of mating pairs were monogamous. This predominantly polygynous mating system contrasts with the primarily monogamous systems of wild congeners and resulted in an effective number of breeders (<em>N_b</em>) less than 30% of the number of penned broodfish. Quarantining particularly prolific males to separate pens during the second year of captivity had little effect on mating behavior, as other males filled their roles. This represents the first documentation of mate choice and fidelity in Guadalupe Bass and provides a template for expected reproductive behavior in a standard hatchery setting. Understanding mating systems, including the effects of captivity on behavior, should enhance restoration efforts, particularly when supplemental stocking programs are involved.

Activity patterns of the water opossum Chironectes minimus in Atlantic Forest rivers of south-eastern Brazil

The activity of the water opossum Chironectes minimus was studied in Atlantic forest rivers in south-eastern Brazil using radiotracking, from October 2004 to October 2008. There were 439 nocturnal fixes of 11 males and four females. Activity patterns of the water opossum were compared among sexes and seasons, using linear and generalized linear mixed models. The water opossum is active mostly at night, showing a unimodal pattern, with activity increasing after sunset and decreasing thereafter along the night. Females were more active in the first quarter of the night and males in the second one. The activity period of males was longer in the dry season, while for females it was longer in the wet season. Sex and season were important determinants of the water opossum activity patterns, mainly because of different sex strategies in a promiscuous/polygynous mating system. However, despite those influences the overall distribution of activity along the night was similar to most Neotropical marsupials. Therefore, similarities in the activity patterns are probably due to phylogenetic constraints and to the absence or weakness of selective pressures modifying the activity of the water opossum.

Population dynamics of the southern short-tailed opossum (Monodelphis dimidiata) in the Pampas of Argentina

The genus Monodelphis is one of the most species rich among Neotropical marsupials. Despite this, little is known about most of the species. One of the most enigmatic species is M. dimidiata, a small terrestrial opossum that inhabits the Pampean region of Argentina, which is suspected to be a semelparous breeder. From 2005 to 2008, we conducted seasonal live trapping in near-pristine marshy grasslands and agroecosystems of the Pampean region in order to evaluate the population trends of this species and the occurrence of semelparity. M. dimidiata was characterised by a low abundance in the study area. The average density was higher in grasslands than in agroecosystems, and it appeared to be influenced by vegetative cover. The onset of the breeding season occurred during spring when the opossums showed a sudden increase in body size. Given that mature individuals were not found beyond autumn, the findings suggest an annual cycle for this species. In addition, this abrupt maturation resulted in a pronounced sexual dimorphism that, together with the strong reproductive seasonality and a likely polygynous mating system, supported previous claims that the species is semelparous. Our results also emphasise the importance of native grassland habitat for the maintenance of stable populations of M. dimidiata.