Effects of nutrient levels on defense against specialist insects in an invasive alligator weed

doi:10.17520/biods.2017301

Abstract

Abstract:

Evolution of Increased Competitive Ability (EICA) has suggested that exotic plants may reduce resource allocation to anti-herbivore defenses and increase allocation to growth due to reduced specialist herbivores in introduced ranges. However, the major limitation for the hypothesis may be that, as important defensive strategies, induced resistance and tolerance were seldom tested and little information is known regarding the evolution of defensive strategies as influenced by resource availability. Nine introduced and nine native populations of Alternanthera philoxeroides were compared for fitness and two morphological traits that influence herbivory, specifically specific stem length (SSL, plants with low SSL have hollow stems favoured by a stem-boring specialist insect Agasicles hygrophila) and root/shoot ratio (RSR) under low and high nutrient availability and with or without A. hygrophila. Introduced populations showed greater total biomass (+14.7%) and lower SSL (-27.5%), demonstrating increased growth and decreased levels of constitutive defense. Tolerance to herbivory was similar between introduced and native populations. SSL plasticity to herbivory was greater in introduced populations under high nutrient levels, and was positively correlated with total biomass. These results suggest that although both functional trait values and plasticity contribute to the adaptation of alligator weeds to a wide range of nutrient availabilities and specialist insect herbivory, introduced populations have evolved higher production of biomass, lower levels of constitutive structural defense, and greater plasticity of structural defense in high nutrient conditions, indicating that the present control practice for A. philoxeroides where introducing A. hygrophila will face great challenges in the future.

http://jtp.cnki.net/bilingual/detail/html/SWDY201712004

Key words: EICA, plant-insect interactions, plasticity, resource availability, induced resistance

Fang Zhou, Zhijie Zhang, Mu Liu, Xiaoyun Pan. Effects of nutrient levels on defense against specialist insects in an invasive alligator weed[J]. Biodiv Sci, 2017, 25(12): 1276-1284.

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URL: https://www.biodiversity-science.net/EN/10.17520/biods.2017301

https://www.biodiversity-science.net/EN/Y2017/V25/I12/1276

Figures/Tables 5

Table 1 ANOVA or ANCOVA of the effects of continental origin, population (pop), nutrient level and herbivory on total biomass, storage root biomass (SRB), root/shoot ratio (RSR), specific stem length (SSL) of Alternanthera philoxeroides.

参数 Source of variation	d.f	F
参数 Source of variation	d.f	总生物量 Total biomass	贮藏根生物量 SRB	根冠比 RSR	比茎长 SSL
采样地 Origin (O)	1, 16	36.76^***	2.07	3.67	51.71^***
种群 Population (Pop)	16, 264	9.01^***	5.69^***	10.05^***	14.03^***
养分 Nutrient (N)	1, 264	1.56	53.41^***	126.82^***	57.00^***
取食 Herbivory (H)	1, 264	16.84^***	7.23^**	10.46^**	3.86
养分 × 取食 (N × H)	1, 264	37.81^***	25.75^***	46.80^***	0.95
采样地 × 养分 (O × N)	1, 264	0.33	0.74	0.10	0.36
采样地 × 取食 (O × H)	1, 264	2.14	0.05	0.09	0.12
采样地 × 养分 × 取食 (O × N × H)	1, 264	0.40	0.01	0.68	5.15^*
养分 × 种群 (N × Pop)	16, 264	1.69	0.57	1.49	1.24
养分 × 取食 × 种群 (N × H × Pop)	16, 264	1.51	0.95	1.49	1.37
协变量 Covariates	1, 287		45.18^***	2.15	23.74^***

Fig. 1 The effects of herbivory by Agasicles hygrophila (with, h+, without, h-) and nutrient level (high, N+, low, N-) on plant total biomass (a), storage root biomass (SRB) (b), root/shoot ratio (RSR) (c), and specific stem length (SSL) (d) of Alternanthera philoxeroides from native (Argentina) and introduced (USA) range. Error bars denote +/- SE.

Fig. 2 The effects of nutrient level (high, N+, low, N-) on tolerance of total biomass (a) and SRB (b) to herbivory by Agasicles hygrophila of Alternanthera philoxeroides from native (Argentina) and introduced (USA) range. Error bars denote +/- SE.

Fig. 3 The effects of nutrient level (high, N+, low, N-) on the plasticity (RTR) of RSR (a) and SSL (b) in response to herbivory by Agasicles hygrophila of Alternanthera philoxeroides from native (Argentina) and introduced (USA) range. Error bars denote +/-SE.

Fig. 4 The correlations between plant fitness (total biomass, SRB), tolerance of total biomass (TBiomass) and SRB (TSRB) to herbivory and functional traits (root/shoot ratio, RSR; specific stem length, SSL), relative trait range of functional traits (RTR for RSR, RTR for SSL) in response to herbivory by Agasicles hygrophila for Alternanthera philoxeroides from native (Argentina) and introduced (USA) range grown under high and low nutrient levels. The solid lines signify positive correlation, and dashed ones mean negative, the thick lines mean significant at P < 0.01, and thin lines at P < 0.05.

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