Photo credit: phys.org

Male Dragonfish Evolve Larger Eyes to Find Mates in the Deep Sea

A recent study from Boston College has unveiled a fascinating adaptation in male dragonfish, revealing that they develop larger eyes as a strategy to locate females in the dark depths of the ocean. This unique form of sexual dimorphism highlights the remarkable evolutionary tactics employed by these creatures, as detailed in the journal Biology Letters.

The male dragonfish, a formidable predator despite its small size, employs several evolutionary adaptations to survive in the deep-sea habitat. Among these adaptations is bioluminescence, which assists not just in hunting but also in communication. Lead researcher Christopher P. Kenaley notes that female dragonfish are significantly less luminous compared to their male counterparts. He describes the findings as “stunning” and emphasizes their importance in understanding the survival mechanisms of these elusive species.

Sexual dimorphism in eye size is an uncommon phenomenon among vertebrates, and Kenaley identifies this as only the second known occurrence in fish, which represent the largest group within this classification. The deep-sea environment, characterized by a lack of light and vast distances between organisms, complicates the mating strategies of its inhabitants. Many deep-sea species, including dragonfish, utilize bioluminescence as a means of attraction and interaction.

Kenaley explains the challenge posed by the bioluminescence dimorphism: while males can produce more light, this creates what he terms a “bioluminescent detection gap.” This paradox means females can detect males at closer ranges than the opposite. In order to bridge this gap, the hypothesis arose that males might have evolved larger eyes capable of capturing more light for improved visibility.

In collaboration with undergraduate students from Boston College and biologist Valentina Di Santo from Stockholm University, the team explored two dragonfish species: Malacosteus niger and Photostomias guernei. Their research focused on the varying sizes of photophores—light-producing organs—between genders.

The researchers modeled visibility distances based on eye size and the amount of light generated by each gender. Results indicated significant detection gaps, ranging from a few meters to over 100 meters. Notably, the males’ larger eyes contribute to closing the gap by approximately 5 meters, which, while modest, is critical in the sparse and competitive deep-sea environment.

Prior studies had suggested the existence of a bioluminescent detection gap, but the Boston College team’s work is the first systematic assessment of its extent and its implications for the evolution of eye size in these species.

Kening concludes that future research may delve into the reasons behind the brighter luminescence observed in male dragonfish compared to females. “Understanding the purpose of luminescent dimorphism is essential,” he stated. “It may serve as a signaling mechanism to indicate the presence of a mate. Further studies are needed to clarify how varying levels of dimorphism influence detection distances.”

More information: Sexually dimorphic eye-size in dragonfishes, a response to a bioluminescent signalling gap, Biology Letters (2024). DOI: 10.1098/rsbl.2024.0165. royalsocietypublishing.org/doi … .1098/rsbl.2024.0165

Citation: When searching for light and a mate in the deep, dark sea, male dragonfish grow larger eyes, scientists discover (2024, July 23) retrieved 23 July 2024 from https://phys.org/news/2024-07-deep-dark-sea-male-dragonfish.html

Source
phys.org