Fitness is defined by the successful passing of an individual’s genes to the next generation. Cephalopods that mate in groups, in particular coastal squid and cuttlefish species, have evolved complex sexual tactics to maximize reproductive success (Morse and Huffard 2019). Through dynamic skin patterning accompanied by typical body postures, individuals send visual signals in the form of displays to potential mates and rival competitors, often engaging in escalating conflicts (Moynihan and Rodaniche 1982, Mather 2016). Moreover, males can simultaneously exhibit receptive color patterns to females and agonistic patterns or even deceptive female patterns to rival males (Brown et al. 2012, Hanlon and Messenger 2018). Therefore, given the diverse number of tactics used to both attract a mate and deter competitors, effective female mate-guarding by consorting males is critical to reproductive success in group-mating cephalopod species. Indeed, literature on coastal squids has described mate-guarding as the pre- and post-copulatory role of males, who are generally observed positioned around the female while she lays eggs in crevices, exhibiting agonistic displays to ward-off rivals to prevent insemination by other males’ sperm (Moynihan and Rodaniche 1982, Mather 2016, Hanlon and Messenger 2018, Morse and Huffard 2019).

The bigfin reef squid Sepioteuthis lessoniana, like the closely related S. sepioidea, is a group-living species that forms shoals and/or schools, and exhibits complex social and sexual behaviors (Moynihan and Rodaniche 1982, Boal and Gonzalez 1998, Sugimoto and Ikeda 2012), including the presence of sneaker males or ‘female mimics’ (Wada et al. 2005). However, to date it has not been the focus of detailed behavioral research in the wild. In this study, we observed S. lessoniana behavior during mating seasons in two distant geographical locations, and found new behavioral elements in the sexual courtship of S. lessoniana. These elements add complexity to existing social interactions and impact sexual strategic choices faced by individuals, with potential implications for the reproductive fitness of both males and females.

Using SCUBA, and after allowing an initial habituation period to the divers, we recorded interactions of individuals and groups in Indonesia (Lembeh, 1.4249° N, 125.2258° E; total 1 h of recording) and Egypt (El Quseir, 26.1014° N, 34.2803° E; total 2 h of recording), between July–September 2013 and May–July 2019, respectively. The focal squids (consort male, female, and main rival male) were distinguished by size, strategy, prominent markings potentially left by attacks, or typical displays (Mather et al. 2010). During filming, we observed that, in addition to females entering crevices to lay eggs as previously described for loliginid squid species (Morse and Huffard 2019), the male also displayed the same behavior (Video S1). Within this context, we annotated when males entered the same crevices where females laid eggs, as well as other notable occurrences, such as visual displays, male-male attacks, and copulations.

We observed that visual displays, in terms of skin and body patterns, were mostly similar to the ones described for S. sepioidea (Moynihan and Rodaniche 1982, Mather 2016, Hanlon and Messenger 2018), with some degree of variation (see Lin et al. 2017). For example, the male stripe display (Fig. 1a, also featured in Fig. 1c), and females exhibiting an almost uniform purple display when sexually receptive (Fig. 1b). Dominant males also used double signaling, exhibiting an agonistic pattern (brown with white flashes) on one side to competing male(s), and a sexual courting pattern to the female on the other (bright purple; Fig. 1c). Notably, during agonistic bouts, we also identified an undescribed display, performed particularly by the dominant male (Fig. 2). During this display, white flashing is often visible (Fig. 2a), complemented sometimes by a zebra color pattern (Fig. 2b, Video S2). Interestingly, the tentacles were markedly exposed and set on a downward direction, with the arms splayed around the mouth or also facing downwards (tentacle exhibition display; Fig. 2). This conspicuous behavior makes the squid highly visible, deterring potential rivals (e.g. Video S1).

We also consistently observed a unique behavior across both sites during egg laying. Of the 15 individual events in which females laid eggs (once or multiple times), 13 were preceded by males entering the same crevice (˜87% probability of laying eggs after male probing; two-tailed exact binomial test: P = 0.005; Fig. 3a). The remaining two events occurred less than 90 s after filming started, which makes it possible that the male could have previously entered the location. Moreover, as only once did a competitor instead of the consort male enter after the female, events are therefore probabilistically dependent as reversing their order would markedly change the probability of occurrence (to ˜6%). When performing this behavior, the male not only hovered close to the crevice, but effectively entered more than half-body length inside and remained for a period of seconds, withdrawing afterwards to give place to the female (Video S1). Each sex exhibited specific skin patterns during probing and laying eggs, both assuming a generally white appearance, but the female with an iridescent green/yellow across the center of the mantle (Fig. 3b), and the male with brown spots around the mantle and a clear blue line (Fig. 3c). In some occasions, sand and debris were seen being ejected out of the crevice when males entered (second event in Video S1). However, it is not clear if this ejection was performed intentionally with the arms/funnel, or if it was an unintentional by-product stemming from fin movement. It is therefore uncertain what is the purpose of this location probing behavior, for example if the male is inspecting the crevice for potential predators that could feed on the eggs, marking a specific site within the location/crevice for the female to lay the eggs, or cleaning the location for the female to deposit the eggs on a stable surface.

Pre-probing locations carries a clear risk for the male, as he abdicates from mate-guarding momentarily and leaves the female vulnerable to the approaches of competing males. When in groups, the main competing male would attempt to seize these opportunities to copulate with the female (with the consort male rushing to position himself between the two, often attacking the competitor, e.g. Video S1), successfully doing so in at least one occasion (Video S3). Evidence suggests that female S. lessoniana can store sperm and may have cryptic female choice of sperm (Morse and Huffard 2019), which could lead to the complete ejection of the consort male’s sperm and, therefore, greatly reduce his reproductive fitness. Conversely, the opportunity of copulating with another male while the male consort is absent may increase the reproductive success of the female (and the competing male), by providing a more diverse gene pool with which to fertilize her eggs.

S. lessoniana is considered to be a species complex composed of several different cryptic species across the Indian and Pacific Oceans, many with overlapping ranges (Cheng et al. 2014). However, distinguishing between cryptic species in the wild is difficult because, while these species are genetically distinct, they are hard to distinguish morphologically. Notably, individuals from considerably distant geographic regions (˜10,000 km between the Red Sea and Indonesia) both show the tentacle exhibition display and the probing behavior. This suggests that either: (1) the individuals observed are the same species, or (2) these behaviors are shared across cryptic species, either as a conserved trait or as a product of convergent evolution. The occurrence of location probing behaviors may also be dependent on habitat features. S. lessoniana have been observed to lay eggs on multiple different types of substrate, from within branching corals to seagrass beds, on mooring lines, and on open sandy substrate (S. H. Cheng, personal observation). In “open environments” where the substrate is visible, such as sandy substrates, location probing may not be present; however, further observations of egg laying are required to understand the potential role that habitat structure may have in shaping male and female behaviors. While its purpose is still unknown, location probing by males seems to be a frequent and important aspect of mating and egg laying in crevices for these populations. From an evolutionary perspective—as this behavior carries potentially high costs to the consort male due to abandoning mate-guarding—there may be significant selective advantages, such as both partners avoiding egg predation. Moreover, location probing by consort males could also be selected for by females, as it additionally provides the female with the opportunity to attain spermatophores from other males. Further observations and studies will help us better understand the ecological (geographical distribution, and habitat specificity) and evolutionary (phylogeny, development, and purpose) drivers behind these behaviors, as well as how they shape individual decision-making in complex social and ecological contexts.

健康的定义是将一个人的基因成功地传递给下一代。成群交配的头足类动物，尤其是沿海鱿鱼和墨鱼物种，已经进化出复杂的性策略，以最大限度地提高繁殖成功率（Morse 和 Huffard 2019）。通过伴随典型身体姿势的动态皮肤图案，个人以展示的形式向潜在配偶和竞争对手发送视觉信号，经常参与升级的冲突（Moynihan 和 Rodaniche 1982，Mather 2016）。此外，雄性可以同时表现出对雌性的接受颜色模式和对雄性的竞争性模式，甚至是欺骗性的雌性模式（Brown et al. 2012 , Hanlon and Messenger 2018）。因此，鉴于用于吸引配偶和威慑竞争者的策略多种多样，通过交配雄性来保护雌性配偶对于群交头足类物种的繁殖成功至关重要。事实上，关于沿海鱿鱼的文献将配偶保护描述为雄性在交配前和交配后的作用，当雌性在裂缝中产卵时，通常观察到雄性围绕在雌性周围，表现出激动的表现以抵御竞争对手，以防止受精其他男性的精子（Moynihan 和 Rodaniche 1982，Mather 2016，Hanlon 和 Messenger 2018，Morse 和 Huffard 2019）。

大鳍礁乌贼Sepioteuthis Lessiana，就像亲缘关系密切的S . sepioidea，是一种群居物种，形成浅滩和/或学校，并表现出复杂的社会和性行为（Moynihan 和 Rodaniche 1982，Boal 和 Gonzalez 1998，Sugimoto 和 Ikeda 2012），包括运动鞋男性或“女性模仿者”的存在'（Wada 等人，2005 年）。然而，迄今为止，它并不是野外详细行为研究的重点。在这项研究中，我们观察到S。 课文在两个遥远的地理位置交配季节的行为，并在S的性求爱中发现了新的行为元素。 课文。这些因素增加了现有社会互动的复杂性，并影响个人面临的性战略选择，对男性和女性的生殖健康有潜在影响。

使用 SCUBA，并在允许潜水员初始适应期后，我们记录了印度尼西亚（Lembeh，北纬 1.4249°，东经 125.2258°；总共记录 1 小时）和埃及（El Quseir，北纬 26.1014°， 34.2803° E；总共记录了 2 小时），分别在 2013 年 7 月至 9 月和 2019 年 5 月至 7 月之间。焦点鱿鱼（配偶雄性、雌性和主要竞争对手雄性）通过大小、策略、攻击可能留下的显着标记或典型展示来区分（Mather 等人，2010 年）。在拍摄过程中，我们观察到，除了雌性进入裂缝产卵，如先前描述的 loliginid 鱿鱼物种 (Morse and Huffard 2019)，雄性也表现出相同的行为（视频 S1）。在这种情况下，我们注释了雄性何时进入雌性产卵的相同裂缝，以及其他值得注意的事件，例如视觉展示、雄性攻击和交配。

我们观察到，就皮肤和身体图案而言，视觉显示与S所描述的大多相似。 sepioidea (Moynihan and Rodaniche 1982 , Mather 2016 , Hanlon and Messenger 2018 )，有一定程度的变异（见 Lin et al. 2017）。例如，雄性条纹显示（图 1a，也在图 1c 中显示），雌性在接受性行为时表现出几乎一致的紫色显示（图 1b）。占主导地位的雄性也使用双重信号，在一侧对竞争雄性表现出一种激动模式（棕色带白色闪光），在另一侧表现出对雌性的性求爱模式（亮紫色；图 1c）。值得注意的是，在激动较量期间，我们还发现了一个未描述的展示，特别是由占主导地位的男性执行的（图 2）。在此显示过程中，通常可以看到白色闪烁（图 2a），有时会辅以斑马色图案（图 2b，视频 S2）。有趣的是，触手明显外露并向下，手臂张开在嘴周围或也朝下（触手展览展示；图2）。

我们还在产卵期间始终观察到两个站点的独特行为。在雌性产卵（一次或多次）的 15 次个体事件中，13 次之前是雄性进入同一缝隙（雄性探查后产卵的概率约为 87%；双尾精确二项式检验：P = 0.005; 图 3a)。剩下的两个事件发生在拍摄开始后不到 90 秒，这使得男性可能之前已经进入了该地点。此外，由于只有一次竞争者而不是配偶男性在女性之后进入，因此事件在概率上是相关的，因为颠倒它们的顺序将显着改变发生的概率（至约 6%）。执行此行为时，雄性不仅在裂缝附近盘旋，而且有效地进入了超过半身长的内部并停留了几秒钟，然后撤回让位给雌性（视频 S1）。每种性别在探测和产卵期间都表现出特定的皮肤图案，两者都呈现出一般的白色外观，但雌性在地幔中央呈虹彩绿色/黄色（图 3b），雄性在地幔周围有棕色斑点和清晰的蓝线（图3c）。在某些情况下，当雄性进入时，看到沙子和碎片从缝隙中喷射出来（视频 S1 中的第二个事件）。然而，目前尚不清楚这种弹射是否是用臂/漏斗故意执行的，或者它是否是由鳍运动引起的无意副产品。因此，不确定这种位置探测行为的目的是什么，例如，如果雄性正在检查裂缝中是否有可能以卵为食的潜在捕食者，在位置/裂缝内标记一个特定的地点供雌性产卵，或清洁雌性将卵放置在稳定的表面上的位置。当雄性进入时，看到沙子和碎片从裂缝中喷射出来（视频 S1 中的第二个事件）。然而，目前尚不清楚这种弹射是否是用臂/漏斗故意执行的，或者它是否是由鳍运动引起的无意副产品。因此，不确定这种位置探测行为的目的是什么，例如，如果雄性正在检查裂缝中是否有可能以卵为食的潜在捕食者，在位置/裂缝内标记一个特定的地点供雌性产卵，或清洁雌性将卵放置在稳定的表面上的位置。当雄性进入时，看到沙子和碎片从裂缝中喷射出来（视频 S1 中的第二个事件）。然而，目前尚不清楚这种弹射是否是用臂/漏斗故意执行的，或者它是否是由鳍运动引起的无意副产品。因此，不确定这种位置探测行为的目的是什么，例如，如果雄性正在检查裂缝中是否有可能以卵为食的潜在捕食者，在位置/裂缝内标记一个特定的地点供雌性产卵，或清洁雌性将卵放置在稳定的表面上的位置。

预先探测的位置对雄性来说存在明显的风险，因为他暂时放弃了配偶保护，让雌性容易受到竞争雄性的接近。当成群结队时，主要的竞争雄性会试图抓住这些机会与雌性交配（配偶雄性急于将自己置于两者之间，经常攻击竞争对手，例如视频 S1），至少在一次成功中这样做了（视频 S3）。有证据表明，女性S . Lessiana可以储存精子，并且可能有神秘的女性精子选择（Morse and Huffard 2019)，这可能导致配偶男性的精子完全射出，从而大大降低其生殖健康。相反，在雄性配偶不在的情况下与另一只雄性交配的机会可能会增加雌性（和竞争雄性）的繁殖成功率，因为​​它提供了一个更多样化的基因库来使她的卵受精。

S. Lessiana被认为是一个物种复合体，由横跨印度洋和太平洋的几种不同的隐匿物种组成，其中许多物种的范围重叠（Cheng 等人，2014 年））。然而，在野外区分隐匿物种很困难，因为虽然这些物种在遗传上不同，但在形态上很难区分。值得注意的是，来自相当远的地理区域（红海和印度尼西亚之间约 10,000 公里）的个体都展示了触手展示展示和探测行为。这表明：（1）观察到的个体是同一物种，或（2）这些行为在隐秘物种之间共享，作为保守性状或趋同进化的产物。位置探测行为的发生也可能取决于栖息地特征。小号。 课文已经观察到在多种不同类型的基质上产卵，从分枝珊瑚内到海草床、系泊绳和开放的沙质基质（SH Cheng，个人观察）。在基底可见的“开放环境”中，例如沙质基底，可能不存在位置探测；然而，需要进一步观察产卵以了解栖息地结构在塑造雄性和雌性行为方面的潜在作用。虽然其目的仍然未知，但雄性的位置探测似乎是这些种群在裂缝中交配和产卵的一个常见且重要的方面。从进化的角度来看——由于放弃配偶保护，这种行为可能会给配偶男性带来高成本——可能有显着的选择优势，例如双方都避免捕食卵子。此外，配偶雄性的位置探测也可以由雌性选择，因为它另外为雌性提供了从其他雄性获取精囊的机会。进一步的观察和研究将帮助我们更好地了解这些行为背后的生态（地理分布和栖息地特异性）和进化（系统发育、发展和目的）驱动因素，以及它们如何在复杂的社会和生态环境中塑造个人决策.