Intrasexual variations in arm morphology related to alternative reproductive tactics in Japanese spear squid
Data files
Dec 26, 2024 version files 286.21 KB
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Data_Hosono_et_al..csv
283.78 KB
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README.md
2.42 KB
Abstract
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.
README: Intrasexual variations in arm morphology related to alternative reproductive tactics in Japanese spear squid
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)