Understanding Evolution and Speciation

Simply put, I am interested in how organisms have evolved to form such a diverse and unique world. However in particular, I am interested in the complex interplay of chemical communication and behavior, and the roles that they have in the evolutionary processes of organismal lineages. Chemical cues are one of the oldest modes of communication in the tree of life – bacteria use it, plants use it, and even we humans use it to navigate our world. However, due to the difficulties of capturing and studying these seemingly intangible chemicals, there is still much to be understood about the dynamic interplay between chemical cues, behavior, and evolution.

Spiders are a unique organism to study chemical communication with because there is still much to be understood about spiders, chemical communication, and evolution. As of current, only 1% of the chemical evolution literature covers that of spiders, and we have only described the pheromone composition of 6 spider families out of the entire spider lineage. There is pioneering work being conducted on better understanding how chemicals are sensed by spiders, what chemicals are used in communication, and how these chemicals have evolved with the spider lineages. The work presented here hopes to take part in the forefronts of this research and uncover the unique mysteries of chemical cues, spiders, and speciation.

Chemical Cues and Evolution

Chemical Cues & Species Recognition

Tetragnatha spiders in Hawaii have adaptively radiated to form over 50 different species across the archipelago. At any given site one can find up to 8 different species living in sympatry yet there is no genomic evidence of hybridization to date. These spiders are exclusively nocturnal with small eyes, suggesting the limited use of visual cues to sense their environment. And unlike many orb-web spiders, Tetragnatha spiders build very thin and delicate orb-webs and do not display any plucking behavior of their web – a common vibratory communication mechanisms used by many orb-weaving spiders. Furthermore, a lineage of the Hawaiian Tetragnatha spider has abandoned web-building altogether and live a cursorial lifestyle. In this study we explore the use of chemical communication by Tetragnatha spiders in species and mate recognition, and examine its role in speciation and adaptive radiation from an organisms to organisms perspective.

Chemical Cues & Substrate Choice

The non-web building, cursorial lineage of the Hawaiian Tetragnatha spiders have adaptively radiated to form several different ecomorphs that each match their day time substrate nearly perfectly. The green spiders are found on green leaves while the brown spiders are found on bark and so on. Furthermore, these ecomorphs have evolved independently across each island where it’s closest relative is a spider of a different ecomorph on the same island (as opposed to the same ecomorph on a separate island). Again, these spiders have small eyes and are exclusively nocturnal, staying extremely stationary in their camouflaged positions during the day. Hence, the use of visual cues in choosing their preferred substrate seems limited and possibly nonexistent. This study hopes to examine the use of chemical cues in substrate choice and further explore the role of chemical cues in the adaptive radiation of this lineage of spiders – this time from an organism to environment perspective.

Mating Behavior & Venom Chemicals

Undergraduate Project: Shuanger Li

In the 2016 Binford, Gillespie, and Maddison paper, they found that the males of the Hawaiian Tetragnatha spiders had a higher molecular weight protein component in their venom cocktail that was lacking in females. They then conducted a series of ecological experiments but concluded that there were no ecological differences that easily explained the differences found in the male and female venom. This project takes this a step farther and investigates the role of venom in the mating behavior and assesses whether the sexual differences found in the venom can be explain by the role of venom in mating for these spiders. Tetragnatha spiders lock jaws when mating and the male fangs come in close proximity to the females body. Thus venom could have an important role in this jaw-locking mating behavior.

Phylogeny and Evolutionary Patterns

Tetragnatha of Ogasawara, Japan

The Ogasawara Islands (also known as the Bonin Islands) are a chain of oceanic islands 1,000km off the coast of Japan that were created from volcanic activity in the middle of the ocean around 48 million years ago. Due to the high percentage of endemic organisms on the archipelago relative to its size, the Ogasawara Islands have been called “the Galapagos of the North West Pacific”, and with much of the flora and fauna mirroring that of Hawaii, there exists a largely unexplored parallel to the rich endemism and adaptive radiations found on the Hawaiian Islands. To date, there is not much known about the life and evolutionary history of the Tetragnatha spiders on the Ogasawara Islands. This work hopes to explore this aspect in order to better help the conservation efforts being conducted to preserve the many endemic organisms found on the island.

Silk Gene Expression

Undergraduate Project: Cory Berger

Spiders are most famous for their outstanding use of silk in their evolutionary history. It is said that silk is one of the reasons why spiders are so successful in this world. However, there is still much that we do not understand about how the silk genes have evolved and changed across the lineage of spiders. Although we do know that certain spiders that do not build webs have lost the mechanisms and silk genes involved in web building, we do not know how this change has happened. By looking across the recently radiated web building and non-web building lineages of Hawaiian Tetragnatha spiders, we hope to better understand the changes web-specific silk gene have undergone during web-loss in a short evolutionary timeframe.

Convergence of Leg Morphology

Undergraduate Project: Anna Wood

Since Darwin’s time, there has been much debate about the predictability of evolution; what really will happen if we replay the so-called “tape of life”? From one perspective, diversification is thought to be dictated by historical contingencies while in the other camp, diversification is thought to be more deterministic. However, we have yet to understand to what extent these two components interplay and interact in the whole evolutionary process. To what extent are things deterministic and which parts are more random? In the non-web building Hawaiian Tetragnatha spiders, we see a repeated evolution of the green ecomorph across the lineage. However, we still do not understand to what degree of convergence these organisms have undergone. Is green-ness the only deterministic trait we can find? Or are there more components of these green spiders that have converged to be similar? In this project we focus on their morphological features and explore this question further.

Conservation and Evolution

Impacts of Invasive Ginger

Undergraduate Project: Gregg Stephenson

Invasive species have a range of ecological impacts and are one of the largest threats to biodiversity and native species. These impacts, especially on ecosystem function, are often complex and not well understood. Preserving these functions and increasing resilience of the ecosystem is a major emphasis in conservation work. Because the impacts on these functions are not well understood it is challenging to make informed management decisions when dealing with invasive species. The Hawaiian Islands have been victim to many invasive species including Hedychium gardnerianum, a ginger plant native to the Himalayas, which has a wide range of impacts as a landscape modifier growing thickly in the understory of much of Hawaii’s lower elevation forests. This project hopes to better understand the effects of this invasive ginger plant on the endemic arthropods of Hawaii.

Research Sites