The Impact of a Seahorse's Size on the Mating Process. Is There a Significant Difference Between the Heights of Brooding Male Hippocampus Reidi as Compared to Non-Brooding Males?

Table of Contents

1. Preface

2. Introduction

3. Body
A. Hypothesis
B.Variables
C. Raw Data
D. Calculations

4. Conclusion and Evaluation

5. Bibliography

1. Preface

Background Information:

As a child, I had found seahorses the most particular out of all marine creatures. I was taught in elementary school that unlike with other species, male seahorses were the carriers of their offspring. I did not understand how a male organism could become pregnant, let alone give birth; that would be a question that would be stuck in my mind for a long time. A few years later, I would learn that female seahorses will deposit eggs into the male’s brood pouch. (Fig. 1) (Danielson, 2002)

Fig. 1

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Hippocampus erectus female transferring eggs to male. Retrieved from (National Aquarium, 2012) https://aqua.org/blog/2012/november/thoughtful-thursdays-chesapeake-bay-lined- seahorses

Although I now knew the process in which the male seahorse got pregnant, I began wondering what sort of advantage seahorses could have by having the males give birth. After researching this sexual role reversal, I discovered that scientists themselves had the same question with no concrete results. There were two potential reasons: the first was that since creating life takes quite a bit of energy, having the male seahorse carry the babies splits the energy load between the two parents. A second reason was that this allows seahorses to reproduce more quickly, since it gives the female seahorse more time to make more eggs; this is logical as seahorses have a low survival rate in the wild. (Texas A&M University, 2008) (Garrick-Maidment, 2004, p. 13). However, since seahorses can deliver up to 1500 eggs, but have an infant survival rate of merely 0.5%, I began wondering what made it so difficult to live to adulthood. (Kateman, 2011) (Danielson, 2002) One factor was that seahorses themselves are extremely fragile, sensitive to even the slightest changes in their environment. I also discovered that most seahorse species are endangered. Over the summer of 2015, I travelled to the west coast and visited the Vancouver Aquarium for the first time, where I saw many different marine animals including the seahorse species Hippocampus erectus. I was fascinated by how sluggish they seemed swimming in the tank; I had always thought that they could move faster. A month later, I travelled to the east coast, this time visiting the Huntsman Marine Science Centre. This time I saw a completely different set of marine species, but I was still drawn to the seahorses. The seahorses at Huntsman were Hippocampus hippocampus, a smaller and less common species of seahorse . Though it was a different species, I saw similarities to those that I saw in Vancouver; the same sluggish movement. The seahorses seemed to prefer to simply cling to vegetation and rest. I spent hours in front of the seahorse tank, examining their feeding and behavioural traits, and bombarding the guides there with questions. I was told that the seahorses had the ability to change colour, and that every morning they would be a pale white since all the lights in the aquarium were closed at 5pm every night. I was doubtful, but after standing for a few hours with a red coat, I noticed that the seahorses had a noticeable red tinge (Fig. 2). When I found out that they were captive bred, I started wondering what differences there were between captive bred seahorses and seahorses from the wild. I pondered the

Fig. 2

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Photocredit: Tony Li, September 2nd, 2015: A Hippocampus hippocampus rests by hanging onto a blade of grass by its tail

differences in size, aggressiveness and feeding habits among other variables. With all the different possibilities, I was excited to begin research. However, when I began searching for data online, I found very little data on seahorses. Since most seahorse species are endangered, there is very little data on them in the wild due to their fragility and conservation status. I quickly realized that I would not be able to find data comparing the seahorse infant mortality rate in the wild as opposed to in captivity, due to the environmental and ethical considerations that have been agreed upon by the global scientific community. (Morgan, 2013, p. 6) After extensive research about seahorses through databases, I found detailed data on Hippocampus reidi concerning the heights of brooding and non-brooding males, and mature and immature females. The data reminded me of my younger interest on male seahorses giving birth, and thus I decided to see if there was a significant height difference between brooding male seahorses as opposed to non-brooding males. The measuring of seahorse height is a quick process, and has not been believed to do any harm for years (Lourie, 2003, p. 5).

2. Introduction

Research Question:

Does Size Give Male Hippocampus reidi an Advantage in Finding Mates?

The term “brooding male” refers to male Hippocampus reidi which were observed to having a bulging brooding pouch containing seahorse eggs. Wild seahorses breed only once a year during their respective breeding seasons. (Texas A&M University, 2008) This allows one to assume that brooding males had found mates and were carrying their offspring, while non-brooding males had not found mates and therefore did not have any offspring to carry. The brooding pouch extends horizontally from seahorses, meaning that its presence will not affect height. In the wild, size can be quite important. Larger male seahorses can intimidate smaller seahorses, especially when competing for a mate. A bigger sized seahorse likely can defend its territory and offspring better than a smaller sized seahorse, thus becoming more appealing for female seahorses. In addition, a larger seahorse could signify an older, more experienced and capable seahorse.

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