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
Water forms 'spine of hydration' around DNA, group finds
26.05.2017 | Cornell University
How herpesviruses win the footrace against the immune system
26.05.2017 | Helmholtz-Zentrum für Infektionsforschung
Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.
Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
26.05.2017 | Life Sciences
26.05.2017 | Life Sciences
26.05.2017 | Physics and Astronomy