DOI: 10.5061/dryad.0000000c7
title: Intrasexual variations in arm morphology related to alternative reproductive tactics in Japanese spear squid

description: The morphology of organisms is closely connected to their ecological
 features and is adapted to their environments. Arms and tentacles,
 appendages of cephalopods, exhibit great morphological variations both
 among and within species based on their ecology, but its intrasexual
 variations remain unexplored. Males of the Japanese spear squid,
 Heterololigo bleekeri, in different size categories pursue alternative
 reproductive tactics (ARTs). Large ‘consort’ males copulate with females
 in a male-parallel position, while small ‘sneaker’ males copulate with
 females in a head-to-head position. These ARTs result in differences in
 mating position and hunting strategy based on body size, leading to a
 hypothesis that ARTs in H. bleekeri may be related to intrasexual
 variations in arm morphology. This hypothesis was tested by analyzing
 stomach contents, arm length, and the number of suckers on each arm with
 squid collected off Miyagi, Japan, during two spawning seasons from
 December to May in 2021–2022 and 2022–2023. Stomach contents clearly
 showed a dietary shift with body growth, with consorts mainly preying on
 fish, and sneakers preying on crustaceans. Relative to body size, sneakers
 had longer arm I–IV and hectocotylus (male modified left arm IV), while
 consorts had shorter tentacles. The number of suckers on each arm tended
 to be lower in sneakers. These results suggest that, in H. bleekeri,
 tentacle morphology is related to feeding habits, and possessing longer
 arms holds some advantage for the sneaker tactic. Detailed behavioral
 observations will be necessary to further explore the adaptive
 significance of arm morphology in this species.
description: # Intrasexual variations in arm morphology related to alternative
 reproductive tactics in Japanese spear squid
 [https://doi.org/10.5061/dryad.0000000c7](https://doi.org/10.5061/dryad.0000000c7) ## Description of the data and file structure Arms and tentacle length, the number of suckers on each arm, and stomach contents were analyzed for consort males, sneaker males, immature males, mature females, and immature females of the Japanese spear squid, *Heterololigo bleekeri* caught throughout the reproductive season. Sneaker males have longer arm I–IV compared to the other group. The dataset (csv) contains sample ID, Mantle length, Reproductive status, Stomach contents, Catch date, Fishing Gear, Freezing/Thawing process, right Arm I–IV length, left Arm IV length, and Number of suckers on the right Arm I–IV of spear squid *Heterololigo bleeker*i collected in the coast of Miyagi prefecture, Japan. ### Files and variables #### File: Data\_Hosono\_et\_al..csv **Description:** Squid data used in the research ##### Variables * ID: sample ID * Mantle Length (mm): length of mantle  * Reproductive Status: reproductive status of individuals. consort male (Consort), sneaker male (Sneaker), immature male (Immature male), mature female (Mature female), immature female (Immature female) * Stomach Contents: stomach contents of each individual. empty stomach (NA) * Catch date: date (yy/mm/dd) on which squid was harvested * Fishing Gear: fishing method used to squid sampling * Freezing/Thawing process: whether squid was frozen and thawed before dissection. Yes (Y), No (N) * right Arm I length (mm): length of right arm I. missing data (NA) * right Arm II length (mm): length of right arm II. missing data (NA) * right Arm III length (mm): length of right arm III. missing data (NA) * right Arm IV length (mm): length of right arm IV. missing data (NA) * left Arm IV length (mm): length of left arm IV. missing data (NA) * right Tentacle length (mm): length of right tentacle. missing data (NA) * Number of suckers on the right Arm I: number of suckers on the right Arm I. missing data (NA) * Number of suckers on the right Arm II: number of suckers on the right Arm II. missing data (NA) * Number of suckers on the right Arm III: number of suckers on the right Arm III. missing data (NA) * Number of suckers on the right Arm IV: number of suckers on the right Arm IV. missing data (NA)