Not Just a Pretty Face: Island Poppies Defend With Prickles

PoppyAlthough the vibrant, waifish petals of the poppy may appear inviting to the casual observer, a closer look reveals a pricklier message: Stay away! To discourage plant eaters like insects and birds from biting into their leafy appendages, many plant species protect themselves with defense mechanisms, like tougher leaves, distasteful latex, and armor made of prickles. Developing these defense features is part of a plant’s natural growth throughout its lifetime. Some plants, however, are able to activate additional protection when faced with attacking herbivores. The authors of a recent PLOS ONE paper investigated these defense mechanisms in two species of poppy currently found in Hawaii, where natural herbivores have long been extinct. The authors’ results reveal that island poppies may have more “nettle” in the face of simulated adversity than previously predicted.

The authors chose two species of poppy for testing, Argemone glauca, a species native to Hawaii, and Argemone mexicana, a species originally hailing from the North American continent and a recent inhabitant of the Hawaiian islands. Both species come pre-equipped with permanent features that may function as defense strategies. However, permanent defenses are costly to maintain for a plant: They divert energy away from other functions, like reproduction and growth, and are therefore an energy investment for the plant. To combat the cost of maintaining a full suite of permanent defenses, some plants respond to attacks from plant eaters only when they occur by activating additional defenses, known as inducible defenses. Unlike defense features that develop throughout the course of a plant’s lifetime, also known as constitutive defenses, inducible defenses are not permanent, only prompted by specific need.

In this study, the researchers simulated the need for additional defenses by subjecting the two species to various “attacks” to see how the poppies would respond. Plants were assigned to one of four random treatment groups:

  1. The control group, which received no treatment
  2. The damage group, where the authors clipped off portions of the leaves
  3. The Jasmonic acid group, where researchers sprayed the leaves with a harmful solution that inhibits growth
  4. And the combination group, where authors defoliated plants first and then sprayed them with Jasmonic acid

The researchers then allowed for two new leaves to grow to ensure that the plants had an adequate amount of time to respond.

Although neither species developed additional leaf toughness or produced more natural latex in response to treatments, both species exhibited increased prickle density on new leaves that grew after treatment. To evaluate prickle density, the authors harvested new leaves and counted all the new prickles on the surfaces of the leaves, excluding prickles found along the leaf edge. They also quantified the leaf area and performed statistical analyses to identify patterns in the various groups.

The authors found that Hawaiian native A. glauca responded more intensely to treatment by developing significantly more prickles than its continental North American counterpart, A. mexicana. The authors report that prickles for A. glauca were 20x more dense and 2.7x higher than A. mexicana.

Plant defenses are selected for over time due to snacking pressures from herbivores. On the Hawaii islands, however, natural herbivores of A. glauca, such as flightless ducks and beetles, are now extinct. The lack of natural predators for island plants has given rise to the idea that island plants have ‘gone soft’ over time. The authors consider A. glauca’s robust response to external attacks evidence that island plants may be better defended than previously thought.

Although it may be impossible to determine whether these island defenses have been selected for by herbivores of the past, no longer present, the inducibility of prickles in A. glauca and A. mexicana demonstrates that these poppies have the mettle to fight back against attackers and snackers.

For more on how herbivores and plants interact, check out this EveryONE blog post on snail mucus.

Citation: Hoan RP, Ormond RA, Barton KE (2014) Prickly Poppies Can Get Pricklier: Ontogenetic Patterns in the Induction of Physical Defense Traits. PLoS ONE 9(5): e96796. doi:10.1371/journal.pone.0096796

Image 1: Agemone glauca by Forest and Kim Starr

The post Not Just a Pretty Face: Island Poppies Defend With Prickles appeared first on EveryONE.

Moonlit Rendezvous: The Box Jellyfish’s Monthly Meet-up in Waikiki

Box Jellyfish

When you think about tropical paradise, Hawaii is often at the top of the list. Waikiki is one of the most iconic Hawaiian beaches on Oahu and is a popular swimming and surfing spot. However, it is also a popular stop for the box jellyfish, one of the most venomous animals in the world. Once a month, about 8 to 12 days after the full moon, the shallow waters of Waikiki beach are temporarily flooded with box jellyfish. They are not coming in for a mai tai under the waning moon; rather, scientists believe that jellyfish reproduce in these waters. This monthly influx creates a hazard to swimmers due to the jellyfish’s painful—and even lethal—stings.

The environmental factors that affect these influxes are not well understood, and learning more about them may help us predict and mitigate the risk that box jellyfish pose to swimmers. Several scientists from Hawaiian institutions published the first long-term (14-year) assessment of the environmental conditions that potentially correlate with box jellyfish population changes in the North Pacific Sub-tropical Gyre.

The researchers surveyed a 400-m section of Waikiki beach during the days jellyfish were present. They counted more than 66,000 jellyfish over 14 years and compared the data to 3 measures of how the climate changes over time, called climate indices; 13 physical and biological variables, such as sea surface temperature and plankton; and seven weather measurements, including wind speed, air temperature, and rainfall.

They confirmed that box jellyfish arrive at Waikiki monthly after each full moon and stay for 2- 4 days. They counted on average 400 jellyfish each month, but the range was quite wide at 5-2,365 individuals. Rather than seeing a net population change over 14 years, researchers observed approximately 4-year periods of increased population count followed by 4-year periods of decreased population count, which coincided with fluctuations in three main environmental factors: oceanic changes in salinity and nutrient availability, called the North Pacific Gyre Oscillation, small organisms’ ability to access nutrients, called primary production, and abundance of small zooplankton.

The researchers suggest that the relationship between environmental fluctuations and jellyfish population changes at Waikiki may result from changes in the availability of food for jellyfish in the ocean around Hawaii, brought about by the North Pacific Gyre Oscillation. During an increase in nutrient availability, phytoplankton populations also increase, meaning more food for jellyfish, allowing them to grow faster and increase their rate of reproduction.

Previous studies have shown that jellyfish populations change due to human-caused disturbances, but this is one of the first long-term studies showing that large-scale climate patterns may also impact box jellyfish populations. Understanding long-term climate and oceanic trends and their effects on jellyfish populations may provide information to develop strategies for avoiding mass stinging events and beach closures at Waikiki and other popular recreation sites in the Pacific.

 

Citation: Chiaverano LM, Holland BS, Crow GL, Blair L, Yanagihara AA (2013) Long-Term Fluctuations in Circalunar Beach Aggregations of the Box Jellyfish Alatina moseri in Hawaii, with Links to Environmental Variability. PLoS ONE 8(10): e77039. doi:10.1371/journal.pone.0077039

Image Credit: Jellyfish by James Brennan Molokai Hawaii