Tue 12 Nov 2019 4.00 pm – Amy Aritsara on “In pursuit of the heteroxyly hypothesis: Sharing tasks between xylem tissues for performance implementation”

In pursuit of the heteroxyly hypothesis: Sharing tasks between xylem tissues for performance implementation

Speaker: Aritsara Amy Ny Aina (College of Forestry, Guangxi University, China)
Date/Time: Tue, 12 Nov 2019, 4 pm
Venue: DBS Conference Room 1 (Block S3 Level 5)

Growing skywards implies that trees have to deal with different kinds of constraints: mechanical support, water transport, resource storage, etc. The heteroxyly hypothesis states that sharing those functions among specialized tissues is more efficient than multifunctional tissues. My study mainly focuses on xylem parenchyma and its contribution to plant hydraulic safety and efficiency. In palms, the ground parenchyma, with its high storage capacity, is vital for the plant to escape from the constraints due to the theoretical vessel tapering and to optimize their water transport efficiency. In basal angiosperms, the axial parenchyma has been believed to hold space and to use large amounts of resources for maintenance, hence trading-off with hydraulic efficiency and safety. However, our findings suggest that it coordinates with the optimization of water transport. In the new era of changing climates, would a xylem with more parenchyma tissue guarantee higher survivorship against environmental stochasticity?

All are welcome.

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Thursday 7 Nov 2019 9.30 am [Qualifying Exam] – Sean Yap on “Reproductive evolution of dung beetles in Southeast Asia”

Speaker: Sean Yap (Graduate Student, Dept. of Biological Sciences, NUS)
Date/Time: Thursday, 7 November 2019: 9.30am
Venue: S3-05-02, DBS Conference Room (S3 Level 5)
Supervisor : Dr Nalini Puniamoorthy

ABSTRACT
Southeast Asia is biodiversity rich, but the role of reproductive isolation via mechanisms of sexual selection remains largely unexplored. Here, we aim to investigate the potential role of sexual selection in reproductive diversification of dung beetles in SEA.

Dung beetles are an incredibly species rich group and provide key ecosystem services in forested and agricultural communities. Globally, these insects are excellent models to investigate speciation by sexual selection because most species and even populations might exhibit stark differences in pre- and postcopulatory sexual traits. However, little is known about reproductive diversification of dung beetles in SEA. There are incomplete records on regional biodiversity and little to no information about genetic structure among widespread populations and morphological variation within species, especially with respect to traits that might establish reproductive barriers to gene flow.

Thus, this research aims to address four complementary research questions to study reproductive evolution in local and regional dung beetle fauna, focusing on two main genera, Onthophagus and Catharsius:

1. What are the morphological and molecular estimates of dung beetle biodiversity in the region?
2. Is postcopulatory sexual selection driving incipient speciation in the Catharsius molossus species complex?
3. Do widespread populations of Onthophagus species differ in sexual selection across SEA?
4. Does nematode diversity and load increase with the intensity of sexual selection across species and populations?

All are welcome.

Fri 8 Nov 2019: 9.00 am [PhD Defense] – Lam Weng Ngai on “Nepenthes: A Model System for the Study of Resource-Mediated Interspecific Interactions”

Nepenthes: A Model System for the Study of Resource-Mediated Interspecific Interactions

Speaker: Lam Weng Ngai (Graduate Student, Dept. of Biological Sciences, NUS)
Date/Time: Friday, 8 November 2019: 9.00am
Venue: S3-05-02, DBS Conference Room (S3 Level 5)
Supervisor: A/P Tan Tiang Wah, Hugh

Carnivorous pitcher plants of the genus Nepenthes bear modified leaves which employ pitfall trap-type mechanisms to capture and digest invertebrate prey. Nutrients obtained from these prey allow Nepenthes to survive in environments that are deficient in these resources. The fluid-filled traps of Nepenthes are also habitats for specialized aquatic organisms known as inquilines, which have been shown to facilitate prey carcass breakdown and thus nutrient sequestration in Nepenthes pitchers.

In this thesis, I use Nepenthes pitcher plants as a model to investigate key topics in ecology relating to interspecific interactions, namely coexistence, facilitation and context dependency.

My thesis is divided into two sections. The first investigates resource-based interactions within this diverse plant genus—specifically, resource competition and facilitation between Nepenthes species—and establishes the key premise of prey resource limitation in Nepenthes species.

The second conditions upon this established premise, but focuses instead on the resource-mediated interactions between the Nepenthes host and its inquilines. Findings of the second section lead me to postulate a previously unexplored mechanism behind resource-mediated positive species interactions.

In the final chapter of the thesis, I investigate this mechanism by formulating a generalizable, consumer-resource type model of what I term as “resource conversion interactions”. Predictions of this model are compared with earlier empirical findings, and synthesis across the whole thesis is attempted.

All are welcome.