A Macroevolutionary Perspective on Multiple Sexual Traits in the Phasianidae (Galliformes)

Table 1

Major hypotheses to explain multiple sexual signals and their predictions extended to the macroevolutionary scale. Terminology largely follows that of Candolin [2] and Bro-Jørgensen [3]. Macroevolutionary predictions inferred from the logic of the hypothesis when not specifically specified in the literature with the assumption that signals of a similar mode are more likely to be redundant in the information they convey, whereas multimodal signals are more likely to communicate multiple messages or to act in concert. Patterns are evaluated for traits involved in mate choice, signaling traits (MC), traits involved in mating competition (Com), and across both sets of characters (Total). Since we were interested in falsification of the hypotheses, we compared our results with the patterns that would contradict (or refute) the hypothesis. Y (yes) indicates that our data refute the hypothesis, N (no) indicates our results cannot refute the hypothesis, and “—” means the data cannot be used to address the hypothesis.

Hypothesis	Description	Extending the hypothesis to the macroevolutionary scale	Macroevolutionary patterns consistent with hypothesis	Macroevolutionary patterns that refute the hypothesis	For each prediction, does our; data refute the hypothesis?
Sexual Signaling (models that can be applied to signals used in inter- and intrasexual signaling)					MC	Com	Total
Multiple messages [4, 5]	Each signal conveys unique information	Selection on each signal is independent, thus the evolutionary trajectories should be as well. Further, we do not expect consistent changes in the number of messages over evolutionary time.	(i) No net accumulation of signals within the same mode of signal	(i) Consistent increase/decrease in number of traits used in signaling	(i) Y	(i) N	(i) Y
			(ii) Independent patterns of loss and gain in different modes	(ii) Increases in traits within a mode	(ii) N	(ii) —	(ii) N
			(iii) Increase in the number of signaling modes	(iii) Correlated trait evolution	(iii) Y	(iii) —	(iii) Y
Redundant/backup signals [4, 5]	All signals convey the same information, the combination reduces errors in communication.	Signals will accumulate over evolutionary time.	(i) Net gain in signaling traits	(i) Net loss of signals	(i) Y	(i) N	(i) Y
			(ii) Net increase in signaling traits within a mode	(ii) Increases in signaling mode that are not accompanied by increases within a mode	(ii) N	(ii) N	(ii) N
Interacting signals: in this category are lumped; receiver psychology hypotheses, alerting signals, and emergent messages, [6–8]	The combination of signals (i.e., their interaction) enhances the communication of a single message.	Signals will accumulate over evolutionary time. However, once an effective complement of signals has evolved no further dynamics are predicted.	(i) Net gain in signaling traits	(i) Net loss of signals	(i) Y	(i) N	(i) Y
			(ii) Net increase in signaling modes	(ii) Replacement of signaling traits	(ii) N	(ii) N	(ii) N
			(iii) Correlated increases in trait modes	(iii) Net increases in signaling traits within a mode.	(iii) N	(iii) —	(iii) N
Multiple/dynamic sensory environments [3]	Because organisms move frequently among different signaling environments (physical and social), alternative signals are required to convey either the same or different messages.	Conveying even a single message across environments favors signaling in more modes; if individuals experience multiple environments, these might arise in a correlated manner; multiple messages increase expected diversity of signals and modes. Loss and gain of signals is expected with environmental change.	(i) Correlated accumulation of signaling traits, both within and among modes	(i) Net gain or loss of signals	(i) Y	(i) N	(i) Y
			(ii) Net increases in signaling traits within a lineage followed by stasis	(ii) No environmental correlates of trait evolution	(ii) —	(ii) —	(ii) —
			(iii) Greater signaling trait diversity in taxa with wider geographic distributions
			(iv) Ongoing gain and loss of traits (i.e., a dynamic equilibrium)
Signaling in mate choice (models that specific incorporate intersexual dynamics)					MC		Total
Rare male effects [9]	Females prefer novel/rare males.	There should be steady replacement of signaling traits over evolutionary time leading; to a dynamic multitrait equilibrium. Signaling mode should have no effect on this process.	(i) No net accumulation of signaling traits or modes.	(i) Net trait or mode accumulation or loss	(i) Y		(i) N
			(ii) Replacement of particular signals while maintaining the same level of dimorphism	(ii) Net diversification within a mode	(ii) N		(ii) N
				(iii) Correlated trait evolution	(iii) Y		(iii) Y
Sexually antagonistic coevolution [10, 11]	Informative signals will degrade in their information content, due to the conflicts between males and females	Informative signals will arise and remain as antes after their information content has been degraded. Thus they remain alongside newly evolved, informative signals	(i) Net accumulation of traits	(i) Trait loss	(i) Y		(i) Y
			(ii) No differences in accumulation rates according to mode	(ii) No net trait accumulation	(ii) N		(ii) N
				(iii) Correlated trait evolution	(iii) Y		(iii) Y
				(iv) Differences in trait accumulation within and among modes	(iv) Y		(iv) Y
Fisher Runaway [4, 12, 13]	Traits arise via a Fisher Runaway process accumulate in lineages	Traits arise and become fixed in species via a Fisher process and therefore tend to accumulate in lineages.	(i) Net accumulation of traits	(i) Trait loss	(i) Y		(i) Y
			(ii) No differences in accumulation rates according to mode	(ii) No net trait accumulation	(ii) Y		(ii) Y
				(iii) Correlated trait evolution	(iii) Y		(iii) Y
				(iv) Differences in trait accumulation within and among modes	(iv) Y		(iv) Y