The idea that horns and antlers evolved in male animals for fighting over mates and territories is well established, but until now no study has been able to come close to explaining every case of female horns in antelope, gazelles and similar species, says Stankowich, a former Darwin Postdoctoral Fellow. But that is just what he and co-author Tim Caro of the University of California Davis have done.
By developing the conspicuousness measure—the product of openness of habitat and shoulder height—as well as female territoriality for this analysis, Stankowich and Caro say they can explain “nearly every instance of horns in female bovids (80 of 82 species).” Their article appears in the current issue of the Proceedings of the Royal Society B. Results suggest that the evolution of horns in these females is driven by natural selection to enhance their ability to defend themselves and their young against predators. The two researchers are the first to specifically test female territoriality as a possible factor, Stankowich notes.
Other variables to explain female weaponry such as body size and group size had been tested before, but Stankowich and Caro pitted all the hypotheses against each other in a statistical analysis and found conspicuousness was the best predictor of the pattern.
In developing the conspicuousness measure, the researchers hypothesized that taller species living in the open are more visible from longer distances and more likely to benefit from horns to defend themselves against predators. “We show that female bovids that are conspicuous to predators because they are large or live in open habitats are far more likely to bear horns than inconspicuous species that can simply rely on being cryptic or hidden in their environment. However, females of some small species like duikers in which females fight over territories also bear horns,” says Stankowich.
Past hypotheses about horns evolving for defense in females predicted that only heavy species are able to defend themselves and would benefit from horns. “Our study shows that it is not necessarily the animal’s size but rather its conspicuousness that counts most, and this is a product of the openness of habitat and body height,” Stankowich adds.
Thus, a medium-sized species living in the desert like a gazelle is very conspicuous and could benefit from horns, but a large species living in the dense jungle like a bushbuck can still remain hidden from predators and have no use for horns. “Different selection pressures are responsible for diverse weaponry in ungulates,” Caro and Stankowich summarize.
Specifically, to investigate factors involved in the evolution of weaponry in female bovids, Stankowich and Caro first categorized the females of 117 bovine species as horned or not. They then used a series of statistical steps to test how well the different predictive variables matched the presence or absence of horns in each species.
Their first analysis tested shoulder height and habitat openness separately, but they also designed a composite measure that accounted for shoulder height while weighting openness more heavily. This exposure metric multiplied a species’ shoulder height measurement factor by mean openness of primary habitat. It allowed bongos, a tall species living in dense forests, to score low on the scale, for example, while medium-sized species such as gazelles score in the middle and tall species in open country such as musk oxen score high.
Pitting the different variables against each other in a series of multiple linear regression models, Stankowich and Caro calculated phylogenetic contrasts for each factor and found that conspicuousness had a statistically significant effect on presence of horns in females and the greatest effect among the five variables. The use of phylogenetic contrasts meant the researchers could take species relatedness with one another into account.
Territoriality among females and body weight of the species also had a significant effect on the presence of horns. That is, large size may reduce escape speed and enhance the need for horns. However, shoulder height and group size did not have an effect.
The two exceptions identified by Stankowich and Caro are the female African bongo, large antelope found in dense forests which use their horns to establish dominance within female groups, and the female mountain anoa, a small water buffalo, which we know very little about but the females may indeed be territorial like other members of its genus (Bubalus). “Our goal was to explain EVERY instance and we think we did just that, given what we know about these two exceptions,” notes Stankowich.
Overall, the two evolutionary biologists believe their findings may be relevant to other female ruminants, but further study is needed.Contact: Ted Stankowich, 413/545-0035; email@example.com
Ted Stankowich | Newswise Science News
Meadows beat out shrubs when it comes to storing carbon
23.11.2017 | Norwegian University of Science and Technology
Migrating Cells: Folds in the cell membrane supply material for necessary blebs
23.11.2017 | Westfälische Wilhelms-Universität Münster
Heat from the friction of rocks caused by tidal forces could be the “engine” for the hydrothermal activity on Saturn's moon Enceladus. This presupposes that...
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
23.11.2017 | Life Sciences
23.11.2017 | Earth Sciences
23.11.2017 | Earth Sciences