Weapon performance drives weapon evolution

Emberts, Zachary; Hwang, Wei Song; Wiens, John J.

doi:10.1098/rspb.2020.2898

Cited by 13 publications

(7 citation statements)

References 54 publications

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“…It is somewhat surprising to find that weapon performance has a lower influence on contest success when compared to weapon size, especially given previous evidence that weapon performance has a substantial influence on contest success [and on weapon evolution (e.g. Lappin & Husak, 2005; Palaoro et al ., 2020; Emberts, Hwang & Wiens, 2021)]. However, interpreting these results requires caution because of the biases and limitations within the available literature.…”

Section: Discussionmentioning

confidence: 94%

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The hidden links between animal weapons, fighting style, and their effect on contest success: a meta‐analysis

Palaoro

Peixoto

2022

Biological Reviews

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In many species that fight over resources, individuals use specialized structures to gain a mechanical advantage over their rivals during contests (i.e. weapons). Although weapons are widespread across animals, how they affect the probability of winning contests is still debated. According to theory, understanding weapon function during contests is essential to: (i) understanding its importance in determining the winner, and (ii) identifying what weapon traits (e.g. weapon length versus shape versus performance) are most relevant for contest success. However, quantitative evaluations of how weapon function affects the extent to which weapon traits influence contest success are still lacking. Here, we first develop an individual‐based model to evaluate how increasing the influence of the weapon in determining the winner translates to differences between winners and losers. Then, we use a meta‐analysis to identify: (i) whether different weapon measures influence contest outcome differently; (ii) how animals use their weapons during fights – i.e. weapon function; and (iii) if weapon function correlates to how weapons influence contest outcome. Our model showed that, as weapons increased the chance of determining the winner, the mean difference between winners and losers also increased. Therefore, in our meta‐analysis we used the mean trait difference between winners and losers as a proxy for the extent to which weapons influence contest success. The literature search identified 49 suitable studies, containing information for 52 species, totalling 107 effect sizes. Four main patterns emerged. First, most of the literature focuses on linear measures of weapons, while performance measures are concentrated on Crustacea and Squamata; other types of measures were rare. Second, differences between winners and losers in linear measurements were greater than differences in performance measurements when all species were combined (and when we used only a subset). Third, species that bear weapons almost always perform visual/tactile displays before engaging in physical contact. And fourth, while the way individuals display their weapons did not influence the importance of weapon size on contest outcomes, fighting style predicted when differences between winners and losers would be higher. Species that used their weapons to push or lift (even when combined with other functions) showed greater differences between winners and losers when compared to species that used their weapons to impact, pierce, pull or squeeze. Overall, our results show that we have an incomplete understanding of animal weapons built mostly on weapon size and a few select taxa. Thus, we should start focusing on measuring weapons according to how they are used during contests and in a wider diversity of species. One way forward is to conduct studies that integrate weapon morphology to weapon function to ensure we are measuring the most ecologically relevant variables.

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Section: Discussionmentioning

confidence: 94%

“…Other species are known to use piercing weapons [e.g. hummingbirds (Rico‐Guevara & Araya‐Salas, 2015) and coreid bugs (Emberts et al ., 2021)] but they were not included in our meta‐analysis because they did not meet our inclusion criteria (e.g. did not involve contests or did not have suitable data).…”

Section: Discussionmentioning

confidence: 99%

The hidden links between animal weapons, fighting style, and their effect on contest success: a meta‐analysis

Palaoro

Peixoto

2022

Biological Reviews

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“…What is even less clear is why selection would favour investment into divergent head shapes and how this might relate to a species ecology (i.e. the divergent context hypothesis; Emberts et al., 2021; Emlen, 2008). Most brentines are associated with dead wood, either as deadwood feeders (i.e.…”

Section: Discussionmentioning

confidence: 99%

The evolution of positive allometry and exaggerated traits in a diverse beetle clade

Painting,

Symonds,

Holwell

2024

Functional Ecology

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Understanding variation in trait allometry and the drivers of variation in sexually selected traits is a major theme in evolutionary biology. The static allometries of sexually selected traits are often positive due to disproportional investment by large individuals into trait size. Comparative studies of weapon allometry are rare, and typically focus on variation along a single dimension (e.g. length), despite weapons often diverging dramatically in shape. Furthermore, studies predominantly focus on groups where weapons have evolved as novel structures (e.g. horns), despite most weapons arising from modifications of existing structures. We test the hypothesis that sexual selection drives variation in static allometry using a phylogenetic comparative approach with 59 brentine weevil species showing remarkable variation in trait exaggeration and sexual size dimorphism (SSD). Contrasting two dimensions of head size exaggeration (a sexually selected trait) and elytron length (a nonsexual trait), positive static allometry was common across both measures of male head size, but not females, and there was positive covariance between male head static allometry and SSD across species. Positive static allometry for male elytron length was less common, but did show positive covariance with SSD, possibly due to the function of wings as compensatory structures for bearing large weapons. Our findings support the hypothesis that sexual selection drives the evolution of allometries both within and among species, and that the modification of existing structures to be used as weapons does not limit the potential for positive static allometry. Read the free Plain Language Summary for this article on the Journal blog.

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“…Alternatively, in some Hemiptera species of the Coreidae family, agonistic interactions involve using spines on the hind legs to damage the rival's wings (Emberts & Wiens, 2021). In these species, both the femur size and the hind legs morphology are important in explaining the extent of the damage caused (Emberts et al, 2021). In fact, a recent review found that weapon size seems to be less important in determining the winner in agonistic interactions in which the weapon is primarily used to cause damage than in interactions in which the weapon is primarily used to push or pull the rival (Palaoro & Peixoto, 2022).…”

Section: Discussionmentioning

confidence: 99%

Do reproductive characteristics of the species explain differences in the investment in weapon size present in males?

2022

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Sexually selected traits, such as male weapons, are highly variable in shape and size across species. However, little is known about the mechanisms that may govern this variation. Because males with greater investment in weapon size tend to win more fights, but also pay higher costs related to weapon development and maintenance, larger weapons should be expected only in species in which victory in male–male fights generate reproductive benefits that outweigh investment costs. Here, we hypothesized that the reproductive characteristics that increase the chances of winners to access females or to fertilize eggs will favor the evolution of larger weapons. To evaluate this hypothesis, we conducted a meta‐analysis using arthropods as model organisms. To measure investment in weapon size, we gathered both Pearson correlation coefficient and the standardized (but non centralized) slope values for the relationship between weapon size and body size. We found that none of the reproductive characteristics we investigated was related to male weapon size. Thus, it seems that greater certainty of accessing a female or fertilizing female eggs with a victory does not modulate the investment in male weapon size. Perhaps the cost–benefit ratio between weapon size investment and reproductive success is not the main factor driving the variation in weapon size.

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Weapon performance drives weapon evolution

Cited by 13 publications

References 54 publications

The hidden links between animal weapons, fighting style, and their effect on contest success: a meta‐analysis

The hidden links between animal weapons, fighting style, and their effect on contest success: a meta‐analysis

The evolution of positive allometry and exaggerated traits in a diverse beetle clade

Do reproductive characteristics of the species explain differences in the investment in weapon size present in males?

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