Size and age at sex change.

<p>Frequency distributions of age (a, b) and standard length (c, d) at sex-change to males (determined from check marks) compared to the distributions of male <i>Halichoeres miniatus</i> at collection from (a, c) Orpheus Island and (b, d) Lizard Island. Age and size distributions of males at collection shown in grey, while age and back-calculated size distributions at sex change (from the otolith check marks) are displayed in white.</p

Growth of males and females by location.

<p>Comparison of mean daily increment widths of male (i.e. females that changed sex to males; black) and female (i.e. non-sex changing fish; grey) <i>Halichoeres miniatus</i> collected from (a) Orpheus Island (n = 18 males, 48 females) (b) and Lizard Island (n = 16 males, 23 females). Mean standard errors are inset.</p

Comparison of males and female encounter rates between locations.

<p>Frequency of encounters per minute (± SE) for <i>Halichoeres miniatus</i> at Orpheus Island (grey) and Lizard Island (white) sampling locations. Based on the 15 min observations of 7 males and 7 females at each location.</p

Comparison of sex-related size and age distributions.

<p>Size (a, c) and age (b, d) distributions for two populations of <i>Halichoeres miniatus</i> at Orpheus Island (a, b) and Lizard Island (c, d). Females are shown as white bars and males as grey.</p

Group size frequency distribution of six <i>Chaetodon</i> spp. at Lizard Island.

<p>Numbers in parentheses indicate sample size of total observations of groups.</p

Predominantly solitary species and solitary <i>C</i>. <i>lunulatus</i> in current study: Sex composition of individuals.

<p>Predominantly solitary species and solitary <i>C</i>. <i>lunulatus</i> in current study: Sex composition of individuals.</p

Dichotomous social systems (pair bonding vs. solitary living) among individuals of <i>Chaetodon lunulatus</i> and among species of <i>Chaetodon</i> at Lizard Island (current study) do not co-vary with other attributes (previously established), controlling for these variables while comparatively studying pair bonding.

<p>Phylogeny data sourced from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194465#pone.0194465.ref061" target="_blank">61</a>], where species clades (CH) and ancestral state nodes and probabilities (in parentheses) are shown. <i>Notes</i>: † = current study. *Parental care is unstudied in Lizard Island populations and is presumed absent based on unequivocal reporting of pelagic spawning within Chaetodontidae. ^Mating systems of these populations at Lizard Island are presumed based on reports at other locations [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194465#pone.0194465.ref063" target="_blank">63</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194465#pone.0194465.ref087" target="_blank">87</a>].</p

Ancestral reconstruction of social behavior in the family Chaetodontidae summarized on a published maximum clade credibility chronogram [61].

<p>Pie charts at nodes represent the posterior probabilities of state reconstructions, summarized from 10,000 stochastic character maps across 1000 randomly sampled topologies from the BEAST posterior distribution of trees [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194465#pone.0194465.ref061" target="_blank">61</a>]. Within the family, pairing is reconstructed as the ancestral character with several subsequent independent transitions to solitary behavior or gregarious grouping and few reversals to pairing (inset). Within the study group (highlighted in blue for solitary and pink for pairing), pairing is ancestral, with one potential origin of solitary sociality in the common ancestor to <i>C</i>. <i>trifascialis</i>, <i>C rainfordi</i>, and <i>C</i>. <i>plebeius</i>. Time axis is in millions of years before present with major epochs identified (P: Pleistocene to Recent epoch).</p

Predominantly pairing species in current study: Sex composition of pairs.

<p>Predominantly pairing species in current study: Sex composition of pairs.</p

Differences in social behaviors between predominantly paired and solitary grouped <i>Chaetodon</i> spp. and <i>C</i>. <i>lunulatus</i> individuals.

<p>(A) Time spent proximate swimming with another conspecific (mean % ± standard error). (B) Time spent parallel swimming with another conspecific (mean % ± standard error). (C) Agonism towards partner vs. non-partner conspecifics among pairs (mean % ± standard error). (D) Percentage of pairs displaying partner fidelity after six weeks. Asterisks indicate significant differences between groups. N/A = not applicable.</p