Answer to an orchid’s puzzling shape hiding in plain sight

The wild orchid Habenaria radiata’s pure white petals resemble a white egret in flight (hence its common name white egret orchid). H. radiata has been loved by people since ancient times but the adaptive significance of the flower’s characteristic jagged shape has been unclear until now. So Kenji Suetsugu and colleagues decided to watch what happens when they chopped the fringes off.

In general, it is thought that petals mainly function as a visual attractant. Hawkmoths, the primary pollinators of the white egret orchid, tend to hover in the air while drinking nectar from flowers and so do not require a place to rest their legs while feeding. This is why the researchers thought the fringes were some sort of visual signal.

A multi-institutional research group has been working for three years to solve this mystery by conducting field experiments in which the feather-like fringe was removed, and detailed behavioural observations of the orchid’s pollinators.

If the fringe is a visual attractant, then removing it should reduce the fruit production of the orchid. To their surprise, the researchers saw no change in the amount of fruit produced. But they did find that the flowers lacking a fringe had fewer healthy seeds. Yet artificial pollination tests on flowers without fringes had no similar problem with seeds, so the lack of healthy seeds had to be related to plant-pollinator interaction.

Taking a closer look, the scientists found that the hawkmoths did not hover continuously while drinking nectar, as thought, but instead grasped onto the petal fringe with their midlegs.

“To the best of our knowledge, this study is the first to investigate experimentally the adaptive significance of long fringes in orchids.” write Suetsugu and colleagues in Ecology.

“The white egret orchid was given its name because its brilliant white petals resemble the bird in flight. According to legend, the soul of a white egret that died was reborn as the much-loved white egret orchid. Nevertheless, it is now evident that fringes primarily stabilize the hawkmoth (the primary pollinator)’s posture, increasing pollen transfer. I am pleased that we have revealed the unexpected adaptive significance that is at the heart of its distinctive fringe.” Professor Suetsugu comments.

More information here.

As population rises, forest area per person plummets

Deforestation effects are being compounded by rising populations, leading to a decline in global forest area per capita of 60%. The study appears in the journal Environmental Research Letters.

A team of researchers, led by Ronald C. Estoque from the Center for Biodiversity and Climate Change, Forestry and Forest Products Research Institute (FFPRI) in Japan, have found that the global forest area has declined by 81.7 million hectares from 1960 to 2019, equivalent to an area of more than 10% of the entire Borneo Island, with gross forest loss (437.3 million hectares) outweighing gross forest gain (355.6 million hectares).  

The team used global land use dataset to examine how global forests have changed over space and time. Consequently, the decline in global forests combined with the increase in global population over the 60-year period has resulted in a decrease of the global forest area per capita by over 60%, from 1.4 hectares in 1960 to 0.5 hectares in 2019. 

Estoque and colleagues write in their article: “The results also revealed that forest transition is not exclusive to the most developed and wealthiest nations. In general, however, there is evidence to show that forest change trajectory was related to socioeconomic conditions of countries: lower income and less developed countries were more associated with forest loss, whereas higher income and more developed countries were more associated with forest gain. There was also a positive relationship between proportion of forest and GDP in the high income and highly developed regions and a significant positive correlation between change in GDP and net forest gain.”

“Overall, our results highlight the need to strengthen the support given to lower income countries, especially in the tropics, to help improve their capacity to minimize or end their forest losses.”

More information here.

Avoid killing weeds with herbicides by zapping them

Researchers from the University of Missouri have been evaluating an alternative to herbicides for weed control. They’ve been studying the effects of a device called The Weed Zapper™ to electrocute eight types of weeds common in soybean crops, including herbicide-resistant waterhemp.

The way the device electrocutes weeds, bit not soybean relies on a height difference between the crop and the weeds. When the weeds stand above the soybean canopy, they brush the electrocution boom, while the crop passes unharmed underneath.

In their article, Schreier and colleagues write: “[I]n order to achieve maximum efficacy, electrocution applications should take place when weed species are at least 60 cm tall and/or when weeds escape above the soybean canopy. A second sequential electrocution pass approximately one week following the first did not always improve weed control, especially when a soybean crop was present. This lends support for the importance of a height differential between the weed and the soybean canopy. Although most weeds were completely controlled following electrocution, giant foxtail, yellow foxtail, barnyardgrass, and waterhemp had some surviving plants.”More information here.