Signal Use by Octopuses in Agonistic Interactions David Scheel, Peter Godfrey-Smith, Matthew Lawrence  Current Biology  Volume 26, Issue 3, Pages 377-382 (February 2016) DOI: 10.1016/j.cub.2015.12.033 Copyright © 2016 Elsevier Ltd Terms and Conditions

Current Biology 2016 26, 377-382DOI: (10.1016/j.cub.2015.12.033) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 Some Behaviors and Actions of Octopus tetricus during Interactions (A) Characteristic mating posture and body patterns. The male (left; body pattern pale with dark eyes) is reaching the right third arm toward the female (right). The male right third arm is pale, and the right second arm is draped over the right third. The female body pattern is mottle. (B) The initiator of an interaction (top), who is dark, extends a reach toward the reactor in that interaction (bottom), who is pale with dark eyes. (C) An octopus displays a dark body pattern, spread arms and web, stand tall, and elevated mantle. (D) Immediately after the display shown in (C), the displaying octopus (left) approaches a second octopus (right; deimatic on the right side of the body with intermediate color on the left side of the body while fleeing backward). See also Movie S1 and Figure S1. Current Biology 2016 26, 377-382DOI: (10.1016/j.cub.2015.12.033) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 2 Relative Darkness of Interacting Octopuses and Behaviors during the Interaction (A) The occurrence of grappling among octopuses similar or differing in darkness. Grapple was significantly less common when the difference in darkness between two interactors was large (mean pixel intensity difference <−60 [initiator darker] or >+40 [reactor darker]; chi-square test, degrees of freedom [df] = 1, χ2 = 3.52, p = 0.037). This comparison uses all available interactions and does not account for repeated measures of the same individual. In a subset of n = 12 interaction pairs, each where interactors were different in darkness in one interaction and similar in another and where each initiator is represented only in a single interaction pair, grapple still occurred significantly less often when interactors were dissimilar than when similar in darkness (paired Wilcoxon signed-rank test, Nsr = 5, z = 1.69, p = 0.046). (B) Darkness of octopuses (mean pixel intensity; more-negative numbers are darker) during behaviors of reactors when an initiator reached toward or approached the reactor. Initiators were darker than reactors at the peak of interactions from which the reactor withdrew (Wilcoxon signed-rank test, n = 15, W = −276, p = 0.000). The reverse (reactors darker) was true during interactions in which the reactor reached in response to the approach of the initiator (n = 22, W = 263, p = 0.000) or stood tall (n = 8, W = 116, p = 0.000). The relative darkness of the two octopuses was not significantly different between the two types of interactions where the reactor did not withdraw (Mann-Whitney U test, reactor stand tall compared to reach, U22,8 = 104, p = 0.475), whereas the relative darkness significantly differed between interactions during which the reactor withdrew or did not withdraw (reactor withdraw compared to reach, U15,22 = 51, p = 0.000; reactor withdraw compared to stand tall, U15,8 = 99, p = 0.011). See also Figure S1. Current Biology 2016 26, 377-382DOI: (10.1016/j.cub.2015.12.033) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 3 Mantle Elevation Was Associated with Darkness and Display from High Ground (A) The darkness of octopuses during stand tall displays was significantly correlated with the highest elevation of their mantle (Fisher’s F statistic, F1,23 = 7.9, p = 0.010). (B) Octopuses with mantle elevations above the horizontal (90°) were significantly more likely to climb to an elevated display position than those whose mantle was below the horizontal (Chi-square test, χ2 = 7.7, df = 1, p = 0.006; the sample size of paired displays by the same individual was too small to account for individual effects). The octopus line drawings illustrate elevation measurements for two example mantle positions, along with the position of the octopus relative to high ground (the main den). See also Movie S1. Current Biology 2016 26, 377-382DOI: (10.1016/j.cub.2015.12.033) Copyright © 2016 Elsevier Ltd Terms and Conditions